JavaScript MCQ Questions
1. What is the correct way to declare a variable in JavaScript?
a. var x = 5;
b. let x = 5;
c. const x = 5;
d. all of the above
Correct Answer:
b. let x = 5;
Explanation: Variables can be declared using var, let, or const in JavaScript, but the recommended way is to use let for variable declarations due to its block scope.
2. How do you write a comment in JavaScript?
php
a. //This is a comment
b. <!–This is a comment–>
c. /*This is a comment*/
d. #This is a comment
Correct Answer:
a. //This is a comment
Explanation: In JavaScript, single-line comments are written with //, and multi-line comments are written with /* */.
3. What is the purpose of the addEventListener method in JavaScript?
a. To create a new element
b. To append an element to the DOM
c. To handle events like clicks or keypresses
d. To define a function
Correct Answer:
c. To handle events like clicks or keypresses
Explanation: addEventListener is used to listen for specific events on HTML elements and execute a function when that event occurs.
4. How can you check the type of a variable in JavaScript?
a. typeOf x;
b. typeof(x);
c. x.typeof();
d. typeof x;
Correct Answer:
d. typeof x;
Explanation: The typeof operator is used to get the data type of a variable in JavaScript.
5. What does the term “hoisting” refer to in JavaScript?
a. Elevating a variable declaration to the top of its scope
b. Creating a loop
c. Moving an element on the web page
d. Declaring a function
Correct Answer:
a. Elevating a variable declaration to the top of its scope
Explanation: Hoisting in JavaScript means that variable and function declarations are moved to the top of their containing scope during the compilation phase.
6. How can you prevent a form from submitting using JavaScript?
a. event.preventSubmit();
b. event.stopDefault();
c. event.preventDefault();
d. form.preventSubmission();
Correct Answer:
c. event.preventDefault();
Explanation: The preventDefault method is used to prevent the default action of an event, such as form submission.
7. What is the purpose of the querySelector method in JavaScript?
a. To select the first element that matches a specified selector
b. To change the document title
c. To create a new HTML element
d. To define a function
Correct Answer:
a. To select the first element that matches a specified selector
Explanation: querySelector is used to select the first HTML element that matches a specified selector.
8. Which operator is used for strict equality in JavaScript?
a. ==
b. ===
c. =
d. !==
Correct Answer:
b. ===
Explanation: The === operator checks both value and type for equality in JavaScript.
9. What is the purpose of the setTimeout function in JavaScript?
a. To create a timer that executes a function after a specified time
b. To set the style of an HTML element
c. To add a delay to a loop
d. To define a recursive function
Correct Answer:
a. To create a timer that executes a function after a specified time
Explanation: setTimeout is used to schedule the execution of a function after a specified delay.
10. How do you check if a variable is an array in JavaScript?
s
a. isArray(x);
b. x.isArray();
c. ArrayCheck(x);
d. typeof Array(x);
Correct Answer:
a. isArray(x);
Explanation: The isArray method is used to check if a variable is an array in JavaScript.
11. What does the this keyword refer to in JavaScript?
a. The current date and time
b. The global object
c. The current function’s scope
d. The calling object
Correct Answer:
d. The calling object
Explanation: In JavaScript, the this keyword refers to the object that is calling the function.
12. How do you convert a string to lowercase in JavaScript?
python
a. str.lowerCase();
b. str.toLower();
c. str.toLowerCase();
d. str.convertLowerCase();
Correct Answer:
c. str.toLowerCase();
Explanation: The toLowerCase method is used to convert a string to lowercase in JavaScript.
13. What is the purpose of the JSON.parse method in JavaScript?
a. To parse HTML documents
b. To convert a JSON string to a JavaScript object
c. To create a JSON string
d. To validate JSON syntax
Correct Answer:
b. To convert a JSON string to a JavaScript object
Explanation: JSON.parse is used to parse a JSON string and convert it into a JavaScript object.
14. How do you remove an element from an array in JavaScript?
c
a. array.remove(index);
b. array.splice(index, 1);
c. array.delete(index);
d. array.pop(index);
Correct Answer:
b. array.splice(index, 1);
Explanation: The splice method is used to remove elements from an array in JavaScript.
15. What is the purpose of the localStorage object in JavaScript?
a. To store session-specific data
b. To store data with no expiration time
c. To store temporary data in a session
d. To store data on the server
Correct Answer:
b. To store data with no expiration time
Explanation: The localStorage object is used to store key/value pairs with no expiration time in web browsers.
16. How can you check if a property exists in an object in JavaScript?
a. object.propertyExists(prop);
b. object.checkProperty(prop);
c. prop in object;
d. object.propertyCheck(prop);
Correct Answer:
c. prop in object;
Explanation: The in operator is used to check if a property exists in an object in JavaScript.
17. What is the purpose of the map function in JavaScript?
a. To create a new array with the results of calling a provided function on every element
b. To rearrange elements in an array
c. To check if every element in an array meets a specified condition
d. To concatenate two arrays
Correct Answer:
a. To create a new array with the results of calling a provided function on every element
Explanation: The map function is used to apply a function to every element in an array and create a new array with the results.
18. How do you handle errors in JavaScript?
a. try/throw/catch
b. catch/throw/finally
c. try/catch/finally
d. throw/try/catch
Correct Answer:
c. try/catch/finally
Explanation: Error handling in JavaScript is typically done using the try, catch, and finally blocks.
19. What is the purpose of the fetch function in JavaScript?
a. To fetch data from a local file
b. To fetch data from a server using AJAX
c. To fetch data from a database
d. To fetch data from the DOM
Correct Answer:
b. To fetch data from a server using AJAX
Explanation: The fetch function is used to make network requests and retrieve data from a server in JavaScript.
20. How can you round a number to the nearest integer in JavaScript?
s
a. round(x);
b. Math.round(x);
c. floor(x);
d. ceil(x);
Correct Answer:
b. Math.round(x);
Explanation: The Math.round method is used to round a number to the nearest integer in JavaScript.
Feel free to ask if you have more questions or if there’s anything else I can assist you with!
21. What is the purpose of the addEventListener method in JavaScript?
a. To attach an event handler to an element
b. To create a new HTML element
c. To change the styling of an element
d. To define a function
Correct Answer:
a. To attach an event handler to an element
Explanation: The addEventListener method is used to attach an event handler function to an HTML element.
22. How do you declare a function in JavaScript?
javascript
a. function myFunction() {}
b. var myFunction = function() {}
c. def myFunction() {}
d. myFunction: function() {}
Correct Answer:
a. function myFunction() {}
Explanation: The function keyword is used to declare a function in JavaScript.
23. What is the purpose of the splice method in JavaScript?
a. To join two arrays
b. To add elements to the end of an array
c. To remove elements from an array
d. To reverse the order of elements in an array
Correct Answer:
c. To remove elements from an array
Explanation: The splice method in JavaScript is used to change the contents of an array by removing or replacing existing elements.
24. How do you declare a constant variable in JavaScript?
java
a. const x = 10;
b. let x = 10;
c. var x = 10;
d. constant x = 10;
Correct Answer:
a. const x = 10;
Explanation: The const keyword is used to declare a constant variable in JavaScript.
25. What is the purpose of the querySelectorAll method in JavaScript?
a. To select the first element that matches a selector
b. To select all elements that match a selector
c. To query the DOM for all elements
d. To retrieve elements by their tag name
Correct Answer:
b. To select all elements that match a selector
Explanation: The querySelectorAll method is used to select all elements that match a specified selector.
26. How do you write a for loop in JavaScript?
a. for (i = 0; i < 5; i++) {}
b. loop (i = 0; i < 5; i++) {}
c. for (i < 5) {}
d. repeat (i = 0; i < 5; i++) {}
Correct Answer:
a. for (i = 0; i < 5; i++) {}
Explanation: The for loop in JavaScript has three parts: initialization, condition, and iteration expression.
27. What is the purpose of the innerHTML property in JavaScript?
a. To change the HTML content of an element
b. To retrieve the value of an input field
c. To check if an element has a specific class
d. To add a new HTML element to the page
Correct Answer:
a. To change the HTML content of an element
Explanation: The innerHTML property is used to set or get the HTML content of an element.
28. How can you create a new array by extracting a subset of elements from an existing array in JavaScript?
a. array.slice(start, end);
b. array.subset(start, end);
c. array.extract(start, end);
d. array.createSubset(start, end);
Correct Answer:
a. array.slice(start, end);
Explanation: The slice method is used to extract a subset of elements from an existing array in JavaScript.
If you have more questions or if there’s anything else I can help you with, feel free to ask!
29. What does the term “closure” refer to in JavaScript?
a. A way to close a web page
b. A function with access to its own scope, plus the outer function’s scope
c. Closing a loop
d. Terminating a script execution
Correct Answer:
b. A function with access to its own scope, plus the outer function’s scope
Explanation: A closure in JavaScript is a function that has access to its own scope, as well as the outer function’s scope, even after the outer function has finished executing.
30. How do you check if a variable is undefined in JavaScript?
javascript
a. if (x === undefined)
b. if (isUndefined(x))
c. if (x == null)
d. if (typeof x === “undefined”)
Correct Answer:
d. if (typeof x === “undefined”)
Explanation: Checking the type using typeof is a common way to determine if a variable is undefined in JavaScript.
31. What is the purpose of the Object.keys method in JavaScript?
a. To get an array of an object’s property names
b. To create a new object
c. To remove keys from an object
d. To check if an object has a specific key
Correct Answer:
a. To get an array of an object’s property names
Explanation: Object.keys is used to return an array of an object’s own enumerable property names.
32. How do you convert a string to a number in JavaScript?
s
a. Number(str);
b. str.toNumber();
c. parseInt(str);
d. str.convertToNumber();
Correct Answer:
a. Number(str);
Explanation: The Number function is commonly used to convert a string to a number in JavaScript.
33. What is the purpose of the filter method in JavaScript?
a. To filter elements in an array based on a condition
b. To create a new array with the results of calling a function on every element
c. To reverse the order of elements in an array
d. To sort elements in an array
Correct Answer:
a. To filter elements in an array based on a condition
Explanation: The filter method is used to create a new array with elements that pass a certain condition.
34. How do you check if a number is an integer in JavaScript?
s
a. Number.isInteger(x);
b. isInteger(x);
c. x.isInteger();
d. typeof x === “integer”;
Correct Answer:
a. Number.isInteger(x);
Explanation: The Number.isInteger method is used to check if a given value is an integer in JavaScript.
35. What is the purpose of the bind method in JavaScript?
a. To create a new array
b. To bind a function to a specific object
c. To add an event listener
d. To concatenate two strings
Correct Answer:
b. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
36. What is the purpose of the async and await keywords in JavaScript?
a. To declare a function as asynchronous and to pause execution until a promise is resolved
b. To create an asynchronous loop
c. To handle exceptions in asynchronous code
d. To define a callback function
Correct Answer:
a. To declare a function as asynchronous and to pause execution until a promise is resolved
Explanation: The async keyword is used to declare a function as asynchronous, and the await keyword is used to pause execution until a promise is resolved.
37. How do you add an element to the end of an array in JavaScript?
c
a. array.addToEnd(element);
b. array.insertLast(element);
c. array.push(element);
d. array.append(element);
Correct Answer:
c. array.push(element);
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
38. What is the purpose of the split method in JavaScript?
vbnet
a. To split a string into an array of substrings based on a specified separator
b. To split an array into multiple arrays
c. To split an object into its properties
d. To split a number into its digits
Correct Answer:
a. To split a string into an array of substrings based on a specified separator
Explanation: The split method is used to divide a string into an array of substrings based on a specified separator.
39. How can you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
40. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
41. How do you remove the last element from an array in JavaScript?
c
a. array.removeLast();
b. array.pop();
c. array.deleteLast();
d. array.splice(-1, 1);
Correct Answer:
b. array.pop();
Explanation: The pop method is used to remove the last element from an array in JavaScript.
42. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
43. How can you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
44. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
45. How can you compare two objects for equality in JavaScript?
s
a. obj1.equals(obj2);
b. obj1 == obj2;
c. JSON.stringify(obj1) === JSON.stringify(obj2);
d. obj1.equals(obj2, deep=true);
Correct Answer:
c. JSON.stringify(obj1) === JSON.stringify(obj2);
Explanation: To compare two objects for equality, you can stringify them using JSON.stringify and then compare the resulting strings.
46. What is the purpose of the Date object in JavaScript?
a. To represent a specific date and time
b. To create a countdown timer
c. To calculate the difference between two dates
d. To format strings
Correct Answer:
a. To represent a specific date and time
Explanation: The Date object in JavaScript is used to represent a specific date and time.
47. How do you check if a value is NaN in JavaScript?
less
a. if (value.isNaN())
b. if (isNaN(value))
c. if (value === NaN)
d. if (value.checkNaN())
Correct Answer:
b. if (isNaN(value))
Explanation: The isNaN function is used to check if a value is NaN in JavaScript.
48. What is the purpose of the fetch function in JavaScript?
a. To fetch data from a local file
b. To fetch data from a server using AJAX
c. To fetch data from the DOM
d. To fetch data from a database
Correct Answer:
b. To fetch data from a server using AJAX
Explanation: The fetch function is used to make network requests and retrieve data from a server in JavaScript.
49. How do you convert a number to a string in JavaScript?
s
a. String(number);
b. number.toString();
c. str(number);
d. convertToString(number);
Correct Answer:
a. String(number);
Explanation: Using the String constructor or the toString method can convert a number to a string in JavaScript.
50. What is the purpose of the Promise object in JavaScript?
a. To create asynchronous functions
b. To handle exceptions
c. To define event listeners
d. To represent a value that might be available now, or in the future, or never
Correct Answer:
d. To represent a value that might be available now, or in the future, or never
Explanation: The Promise object is used for asynchronous programming in JavaScript, representing a value that might be available now, or in the future, or never.
Feel free to ask if you have more questions or if there’s anything else I can assist you with!
51. What is the purpose of the addEventListener method in JavaScript?
a. To create a new element
b. To append an element to the DOM
c. To handle events like clicks or keypresses
d. To define a function
Correct Answer:
c. To handle events like clicks or keypresses
Explanation: The addEventListener method is used to attach an event handler function to an HTML element, enabling it to handle events like clicks or keypresses.
52. How do you declare a class in JavaScript?
vbnet
a. class MyClass {}
b. var MyClass = new class {}
c. function MyClass() {}
d. MyClass: class {}
Correct Answer:
a. class MyClass {}
Explanation: The class keyword is used to declare a class in JavaScript.
53. What does the term “strict mode” mean in JavaScript?
a. A way to execute code more slowly for testing purposes
b. A mode that enforces a stricter set of rules in the language
c. A mode for creating secure connections to databases
d. A mode that allows for more lenient syntax checking
Correct Answer:
b. A mode that enforces a stricter set of rules in the language
Explanation: Strict mode in JavaScript enables a stricter set of rules and helps catch common coding errors.
54. How do you create a copy of an array in JavaScript?
php
a. array.copy();
b. array.clone();
c. array.slice();
d. array.copyArray();
Correct Answer:
c. array.slice();
Explanation: The slice method can be used to create a shallow copy of an array in JavaScript.
55. What is the purpose of the bind method in JavaScript?
a. To bind a function to a specific object
b. To create a new array
c. To add an event listener
d. To concatenate two strings
Correct Answer:
a. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
56. How can you check if a variable is an object in JavaScript?
s
a. objectCheck(x);
b. x.isObject();
c. typeof x === “object”;
d. isObject(x);
Correct Answer:
c. typeof x === “object”;
Explanation: Checking the type using typeof is a common way to determine if a variable is an object in JavaScript.
57. What is the purpose of the Math.random function in JavaScript?
a. To generate a random number between 1 and 10
b. To round a number to the nearest integer
c. To generate a random floating-point number between 0 and 1
d. To calculate the square root of a number
Correct Answer:
c. To generate a random floating-point number between 0 and 1
Explanation: The Math.random function in JavaScript is used to generate a random floating-point number between 0 (inclusive) and 1 (exclusive).
58. How do you remove all elements from an array in JavaScript?
c
a. array.clear();
b. array.removeAll();
c. array = [];
d. array.removeElements();
Correct Answer:
c. array = [];
Explanation: Assigning an empty array to the existing array is a simple way to remove all elements from it in JavaScript.
59. What is the purpose of the Array.isArray method in JavaScript?
a. To check if a variable is an array
b. To create a new array
c. To filter elements in an array
d. To reverse the order of elements in an array
Correct Answer:
a. To check if a variable is an array
Explanation: The Array.isArray method is used to check if a variable is an array in JavaScript.
60. How do you convert a string to an array of characters in JavaScript?
python
a. str.toArray();
b. Array.from(str);
c. str.split(”);
d. stringToCharArray(str);
Correct Answer:
c. str.split(”);
Explanation: Using the split method with an empty string as the separator can convert a string to an array of characters in JavaScript.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
61. What is the purpose of the arguments object in JavaScript?
a. To pass arguments to a function
b. To access all arguments passed to a function
c. To create a new object
d. To declare variables in a function
Correct Answer:
b. To access all arguments passed to a function
Explanation: The arguments object in JavaScript allows a function to access all the arguments passed to it, even if they were not defined as parameters.
62. How do you check if a string contains a specific substring in JavaScript?
python
a. str.hasSubstring(‘sub’);
b. str.includes(‘sub’);
c. str.contains(‘sub’);
d. str.indexOf(‘sub’) !== -1;
Correct Answer:
b. str.includes(‘sub’);
Explanation: The includes method is used to check if a string contains a specific substring in JavaScript.
63. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
64. How can you iterate over the properties of an object in JavaScript?
javascript
a. for (let key in obj) {}
b. obj.forEach((key, value) => {})
c. for (let value of obj) {}
d. obj.map((key, value) => {})
Correct Answer:
a. for (let key in obj) {}
Explanation: The for…in loop is commonly used to iterate over the properties of an object in JavaScript.
65. What is the purpose of the JSON.stringify method in JavaScript?
a. To parse a JSON string
b. To convert an object to a JSON string
c. To check if a string is valid JSON
d. To create a new JSON object
Correct Answer:
b. To convert an object to a JSON string
Explanation: The JSON.stringify method is used to convert an object to a JSON-formatted string in JavaScript.
66. How can you round a number to a specific number of decimal places in JavaScript?
s
a. Math.roundToDecimal(x, 2);
b. x.round(2);
c. x.toFixed(2);
d. round(x, 2);
Correct Answer:
c. x.toFixed(2);
Explanation: The toFixed method is used to round a number to a specific number of decimal places in JavaScript.
67. What is the purpose of the isNaN function in JavaScript?
a. To check if a variable is not a number
b. To check if a variable is a number
c. To convert a string to a number
d. To round a number
Correct Answer:
a. To check if a variable is not a number
Explanation: The isNaN function is used to check if a variable is not a number in JavaScript.
68. How do you convert a string to uppercase in JavaScript?
s
a. str.upperCase();
b. str.toUpper();
c. str.toUpperCase();
d. convertToUpper(str);
Correct Answer:
c. str.toUpperCase();
Explanation: The toUpperCase method is used to convert a string to uppercase in JavaScript.
69. What is the purpose of the forEach method in JavaScript?
a. To create a new array with the results of calling a function on every element
b. To loop over the elements of an array and execute a function
c. To filter elements in an array based on a condition
d. To reverse the order of elements in an array
Correct Answer:
b. To loop over the elements of an array and execute a function
Explanation: The forEach method is used to loop over the elements of an array and execute a function for each element.
70. How do you remove the first element from an array in JavaScript?
c
a. array.removeFirst();
b. array.shift();
c. array.deleteFirst();
d. array.splice(0, 1);
Correct Answer:
b. array.shift();
Explanation: The shift method is used to remove the first element from an array in JavaScript.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
71. What is the purpose of the setTimeout function in JavaScript?
a. To create a timer that executes a function after a specified time
b. To set the style of an HTML element
c. To add a delay to a loop
d. To define a recursive function
Correct Answer:
a. To create a timer that executes a function after a specified time
Explanation: The setTimeout function is used to schedule the execution of a function after a specified delay.
72. How do you check if a variable is a function in JavaScript?
s
a. isFunction(x);
b. typeof x === “function”;
c. x.isFunction();
d. functionCheck(x);
Correct Answer:
b. typeof x === “function”;
Explanation: Checking the type using typeof is a common way to determine if a variable is a function in JavaScript.
73. What is the purpose of the splice method in JavaScript?
a. To join two arrays
b. To add elements to the end of an array
c. To remove elements from an array
d. To reverse the order of elements in an array
Correct Answer:
c. To remove elements from an array
Explanation: The splice method in JavaScript is used to change the contents of an array by removing or replacing existing elements.
74. How do you declare a variable in JavaScript?
a. let x = 10;
b. var x = 10;
c. const x = 10;
d. All of the above
Correct Answer:
d. All of the above
Explanation: In JavaScript, you can declare a variable using let, var, or const.
75. What is the purpose of the map function in JavaScript?
a. To create a new array with the results of calling a provided function on every element
b. To rearrange elements in an array
c. To check if every element in an array meets a specified condition
d. To concatenate two arrays
Correct Answer:
a. To create a new array with the results of calling a provided function on every element
Explanation: The map function is used to apply a function to every element in an array and create a new array with the results.
76. How do you convert a number to a string in JavaScript?
s
a. number.toString();
b. String(number);
c. str(number);
d. convertToString(number);
Correct Answer:
b. String(number);
Explanation: Using the String constructor or the toString method can convert a number to a string in JavaScript.
77. What is the purpose of the filter method in JavaScript?
a. To create a new array with the results of calling a function on every element
b. To rearrange elements in an array
c. To filter elements in an array based on a condition
d. To sort elements in an array
Correct Answer:
c. To filter elements in an array based on a condition
Explanation: The filter method is used to create a new array with elements that pass a certain condition.
78. How do you check if a value is an array in JavaScript?
s
a. isArray(x);
b. x.isArray();
c. ArrayCheck(x);
d. typeof Array(x);
Correct Answer:
a. isArray(x);
Explanation: The isArray method is used to check if a value is an array in JavaScript.
79. What is the purpose of the Object.keys method in JavaScript?
a. To get an array of an object’s property names
b. To create a new object
c. To remove keys from an object
d. To check if an object has a specific key
Correct Answer:
a. To get an array of an object’s property names
Explanation: Object.keys is used to return an array of an object’s own enumerable property names.
80. How do you declare a constant variable in JavaScript?
java
a. const x = 10;
b. let x = 10;
c. var x = 10;
d. constant x = 10;
Correct Answer:
a. const x = 10;
Explanation: The const keyword is used to declare a constant variable in JavaScript.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
81. What is the purpose of the addEventListener method in JavaScript?
a. To create a new element
b. To append an element to the DOM
c. To handle events like clicks or keypresses
d. To define a function
Correct Answer:
c. To handle events like clicks or keypresses
Explanation: The addEventListener method is used to attach an event handler function to an HTML element, enabling it to handle events like clicks or keypresses.
82. How do you declare a function in JavaScript?
javascript
a. function myFunction() {}
b. var myFunction = function() {}
c. def myFunction() {}
d. myFunction: function() {}
Correct Answer:
a. function myFunction() {}
Explanation: The function keyword is used to declare a function in JavaScript.
83. What is the purpose of the splice method in JavaScript?
a. To join two arrays
b. To add elements to the end of an array
c. To remove elements from an array
d. To reverse the order of elements in an array
Correct Answer:
c. To remove elements from an array
Explanation: The splice method in JavaScript is used to change the contents of an array by removing or replacing existing elements.
84. How do you handle errors in JavaScript?
javascript
a. try/throw/catch
b. catch/throw/finally
c. try/catch/finally
d. throw/try/catch
Correct Answer:
c. try/catch/finally
Explanation: Error handling in JavaScript is typically done using the try, catch, and finally blocks.
85. What is the purpose of the fetch function in JavaScript?
a. To fetch data from a local file
b. To fetch data from a server using AJAX
c. To fetch data from a database
d. To fetch data from the DOM
Correct Answer:
b. To fetch data from a server using AJAX
Explanation: The fetch function is used to make network requests and retrieve data from a server in JavaScript.
86. How can you round a number to the nearest integer in JavaScript?
s
a. round(x);
b. Math.round(x);
c. floor(x);
d. ceil(x);
Correct Answer:
b. Math.round(x);
Explanation: The Math.round method is used to round a number to the nearest integer in JavaScript.
87. What is the purpose of the addEventListener method in JavaScript?
a. To attach an event handler to an element
b. To create a new HTML element
c. To change the styling of an element
d. To define a function
Correct Answer:
a. To attach an event handler to an element
Explanation: The addEventListener method is used to attach an event handler function to an HTML element.
88. How do you declare a function in JavaScript?
javascript
a. function myFunction() {}
b. var myFunction = function() {}
c. def myFunction() {}
d. myFunction: function() {}
Correct Answer:
a. function myFunction() {}
Explanation: The function keyword is used to declare a function in JavaScript.
89. What is the purpose of the splice method in JavaScript?
a. To join two arrays
b. To add elements to the end of an array
c. To remove elements from an array
d. To reverse the order of elements in an array
Correct Answer:
c. To remove elements from an array
Explanation: The splice method in JavaScript is used to change the contents of an array by removing or replacing existing elements.
90. How do you handle errors in JavaScript?
javascript
a. try/throw/catch
b. catch/throw/finally
c. try/catch/finally
d. throw/try/catch
Correct Answer:
c. try/catch/finally
Explanation: Error handling in JavaScript is typically done using the try, catch, and finally blocks.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
91. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
92. How do you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
93. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
94. How do you check if a number is an integer in JavaScript?
s
a. Number.isInteger(x);
b. isInteger(x);
c. x.isInteger();
d. typeof x === “integer”;
Correct Answer:
a. Number.isInteger(x);
Explanation: The Number.isInteger method is used to check if a given value is an integer in JavaScript.
95. What is the purpose of the bind method in JavaScript?
a. To create a new array
b. To bind a function to a specific object
c. To add an event listener
d. To concatenate two strings
Correct Answer:
b. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
96. What is the purpose of the async and await keywords in JavaScript?
a. To declare a function as asynchronous and to pause execution until a promise is resolved
b. To create an asynchronous loop
c. To handle exceptions in asynchronous code
d. To define a callback function
Correct Answer:
a. To declare a function as asynchronous and to pause execution until a promise is resolved
Explanation: The async keyword is used to declare a function as asynchronous, and the await keyword is used to pause execution until a promise is resolved.
97. How do you add an element to the end of an array in JavaScript?
c
a. array.addToEnd(element);
b. array.insertLast(element);
c. array.push(element);
d. array.append(element);
Correct Answer:
c. array.push(element);
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
98. What is the purpose of the split method in JavaScript?
vbnet
a. To split a string into an array of substrings based on a specified separator
b. To split an array into multiple arrays
c. To split an object into its properties
d. To split a number into its digits
Correct Answer:
a. To split a string into an array of substrings based on a specified separator
Explanation: The split method is used to divide a string into an array of substrings based on a specified separator.
99. How can you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
100. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
Feel free to ask if you have more questions or if there’s anything else I can assist you with!
101. How do you remove the last element from an array in JavaScript?
c
a. array.removeLast();
b. array.pop();
c. array.deleteLast();
d. array.splice(-1, 1);
Correct Answer:
b. array.pop();
Explanation: The pop method is used to remove the last element from an array in JavaScript.
102. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
103. How can you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
104. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
105. How do you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
106. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
107. How do you remove the first element from an array in JavaScript?
c
a. array.removeFirst();
b. array.shift();
c. array.deleteFirst();
d. array.splice(0, 1);
Correct Answer:
b. array.shift();
Explanation: The shift method is used to remove the first element from an array in JavaScript.
108. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
109. How can you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
110. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
111. What is the purpose of the indexOf method in JavaScript?
a. To find the index of the first occurrence of a value in an array
b. To create a new array
c. To check if an element exists in an array
d. To concatenate two arrays
Correct Answer:
a. To find the index of the first occurrence of a value in an array
Explanation: The indexOf method is used to find the index of the first occurrence of a specified value in an array.
112. How do you reverse the order of elements in an array in JavaScript?
c
a. array.reverse();
b. array.flip();
c. array.rotate();
d. array.rearrange();
Correct Answer:
a. array.reverse();
Explanation: The reverse method is used to reverse the order of elements in an array in JavaScript.
113. What is the purpose of the parseFloat function in JavaScript?
a. To convert a string to a floating-point number
b. To round a number to the nearest integer
c. To check if a variable is a float
d. To create a new float object
Correct Answer:
a. To convert a string to a floating-point number
Explanation: The parseFloat function is used to convert a string to a floating-point number in JavaScript.
114. How do you add a class to an HTML element using JavaScript?
csharp
a. element.addClass(“new-class”);
b. element.className = “new-class”;
c. element.add(“new-class”);
d. element.appendClass(“new-class”);
Correct Answer:
b. element.className = “new-class”;
Explanation: Assigning a new value to the className property is one way to add a class to an HTML element using JavaScript.
115. What is the purpose of the includes method in JavaScript?
a. To create a new array with the results of calling a function on every element
b. To check if a string contains a specific substring
c. To filter elements in an array based on a condition
d. To sum the elements of an array
Correct Answer:
b. To check if a string contains a specific substring
Explanation: The includes method is used to check if a string contains a specific substring in JavaScript.
116. How can you check if a variable is undefined in JavaScript?
javascript
a. isUndefined(x);
b. x.isDefined();
c. x === undefined;
d. typeof x === “undefined”;
Correct Answer:
c. x === undefined;
Explanation: Checking if a variable is equal to undefined is a common way to verify if it is undefined in JavaScript.
117. What is the purpose of the textContent property in JavaScript?
a. To set the text content of an HTML element
b. To retrieve the HTML content of an element
c. To get or set the text content of an element
d. To append text to an element
Correct Answer:
c. To get or set the text content of an element
Explanation: The textContent property is used to get or set the text content of an HTML element in JavaScript.
118. How do you create a new element in the DOM using JavaScript?
javascript
a. document.createElement(“newElement”);
b. document.add(“newElement”);
c. document.newElement(“newElement”);
d. document.create(“newElement”);
Correct Answer:
a. document.createElement(“newElement”);
Explanation: The createElement method is used to create a new HTML element in the DOM using JavaScript.
119. What is the purpose of the splice method in JavaScript?
a. To join two arrays
b. To add elements to the end of an array
c. To remove elements from an array
d. To reverse the order of elements in an array
Correct Answer:
c. To remove elements from an array
Explanation: The splice method in JavaScript is used to change the contents of an array by removing or replacing existing elements.
120. How do you declare a variable in JavaScript?
a. let x = 10;
b. var x = 10;
c. const x = 10;
d. All of the above
Correct Answer:
d. All of the above
Explanation: In JavaScript, you can declare a variable using let, var, or const.
Feel free to ask if you have more questions or if there’s anything else I can assist you with!
121. What is the purpose of the JSON.parse method in JavaScript?
a. To stringify an object
b. To convert a JSON string to an object
c. To create a new JSON object
d. To check if a string is valid JSON
Correct Answer:
b. To convert a JSON string to an object
Explanation: The JSON.parse method is used to convert a JSON-formatted string to a JavaScript object.
122. How do you remove an event listener in JavaScript?
less
a. element.removeEventListener(“click”, myFunction);
b. element.removeEvent(“click”, myFunction);
c. element.off(“click”, myFunction);
d. element.detachEvent(“click”, myFunction);
Correct Answer:
a. element.removeEventListener(“click”, myFunction);
Explanation: The removeEventListener method is used to remove an event listener in JavaScript.
123. What is the purpose of the toFixed method in JavaScript?
a. To round a number to the nearest integer
b. To round a number to a specific number of decimal places
c. To convert a number to a string
d. To check if a number is an integer
Correct Answer:
b. To round a number to a specific number of decimal places
Explanation: The toFixed method is used to round a number to a specific number of decimal places in JavaScript.
124. How do you convert a string to lowercase in JavaScript?
s
a. str.lower();
b. str.toLower();
c. str.toLowerCase();
d. convertToLower(str);
Correct Answer:
c. str.toLowerCase();
Explanation: The toLowerCase method is used to convert a string to lowercase in JavaScript.
125. What is the purpose of the push method in JavaScript?
a. To add an element to the beginning of an array
b. To add an element to the end of an array
c. To remove the last element from an array
d. To check if an array is empty
Correct Answer:
b. To add an element to the end of an array
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
126. How do you declare a constant variable in JavaScript?
java
a. const x = 10;
b. let x = 10;
c. var x = 10;
d. constant x = 10;
Correct Answer:
a. const x = 10;
Explanation: The const keyword is used to declare a constant variable in JavaScript.
127. What is the purpose of the Math.random function in JavaScript?
a. To generate a random integer
b. To round a number to the nearest integer
c. To generate a random floating-point number
d. To check if a number is NaN
Correct Answer:
c. To generate a random floating-point number
Explanation: The Math.random function is used to generate a random floating-point number between 0 (inclusive) and 1 (exclusive) in JavaScript.
128. How do you concatenate two arrays in JavaScript?
c
a. array.concat(array2);
b. array + array2;
c. array.join(array2);
d. array.combine(array2);
Correct Answer:
a. array.concat(array2);
Explanation: The concat method is used to concatenate two arrays in JavaScript.
129. What is the purpose of the slice method in JavaScript?
a. To divide an array into two separate arrays
b. To remove elements from an array
c. To create a shallow copy of an array
d. To reverse the order of elements in an array
Correct Answer:
c. To create a shallow copy of an array
Explanation: The slice method is used to create a shallow copy of an array in JavaScript.
130. How do you convert a number to a string in JavaScript?
s
a. number.toString();
b. String(number);
c. str(number);
d. convertToString(number);
Correct Answer:
b. String(number);
Explanation: Using the String constructor or the toString method can convert a number to a string in JavaScript.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
131. What is the purpose of the filter method in JavaScript?
a. To create a new array with the results of calling a function on every element
b. To rearrange elements in an array
c. To filter elements in an array based on a condition
d. To sort elements in an array
Correct Answer:
c. To filter elements in an array based on a condition
Explanation: The filter method is used to create a new array with elements that pass a certain condition.
132. How do you declare a function in JavaScript?
javascript
a. function myFunction() {}
b. var myFunction = function() {}
c. def myFunction() {}
d. myFunction: function() {}
Correct Answer:
a. function myFunction() {}
Explanation: The function keyword is used to declare a function in JavaScript.
133. What is the purpose of the splice method in JavaScript?
a. To join two arrays
b. To add elements to the end of an array
c. To remove elements from an array
d. To reverse the order of elements in an array
Correct Answer:
c. To remove elements from an array
Explanation: The splice method in JavaScript is used to change the contents of an array by removing or replacing existing elements.
134. How do you handle errors in JavaScript?
javascript
a. try/throw/catch
b. catch/throw/finally
c. try/catch/finally
d. throw/try/catch
Correct Answer:
c. try/catch/finally
Explanation: Error handling in JavaScript is typically done using the try, catch, and finally blocks.
135. What is the purpose of the fetch function in JavaScript?
a. To fetch data from a local file
b. To fetch data from a server using AJAX
c. To fetch data from a database
d. To fetch data from the DOM
Correct Answer:
b. To fetch data from a server using AJAX
Explanation: The fetch function is used to make network requests and retrieve data from a server in JavaScript.
136. How can you round a number to the nearest integer in JavaScript?
s
a. round(x);
b. Math.round(x);
c. floor(x);
d. ceil(x);
Correct Answer:
b. Math.round(x);
Explanation: The Math.round method is used to round a number to the nearest integer in JavaScript.
137. What is the purpose of the addEventListener method in JavaScript?
a. To create a new element
b. To append an element to the DOM
c. To handle events like clicks or keypresses
d. To define a function
Correct Answer:
c. To handle events like clicks or keypresses
Explanation: The addEventListener method is used to attach an event handler function to an HTML element, enabling it to handle events like clicks or keypresses.
138. How do you check if a variable is undefined in JavaScript?
javascript
a. isUndefined(x);
b. x.isDefined();
c. x === undefined;
d. typeof x === “undefined”;
Correct Answer:
c. x === undefined;
Explanation: Checking if a variable is equal to undefined is a common way to verify if it is undefined in JavaScript.
139. What is the purpose of the JSON.stringify method in JavaScript?
a. To parse a JSON string
b. To convert an object to a JSON string
c. To create a new JSON object
d. To check if a string is valid JSON
Correct Answer:
b. To convert an object to a JSON string
Explanation: The JSON.stringify method is used to convert an object to a JSON-formatted string in JavaScript.
140. How do you remove the first element from an array in JavaScript?
c
a. array.removeFirst();
b. array.shift();
c. array.deleteFirst();
d. array.splice(0, 1);
Correct Answer:
b. array.shift();
Explanation: The shift method is used to remove the first element from an array in JavaScript.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
141. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
142. How do you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
143. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
144. How do you check if a number is an integer in JavaScript?
s
a. Number.isInteger(x);
b. isInteger(x);
c. x.isInteger();
d. typeof x === “integer”;
Correct Answer:
a. Number.isInteger(x);
Explanation: The Number.isInteger method is used to check if a given value is an integer in JavaScript.
145. What is the purpose of the bind method in JavaScript?
a. To create a new array
b. To bind a function to a specific object
c. To add an event listener
d. To concatenate two strings
Correct Answer:
b. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
146. What is the purpose of the async and await keywords in JavaScript?
a. To declare a function as asynchronous and to pause execution until a promise is resolved
b. To create an asynchronous loop
c. To handle exceptions in asynchronous code
d. To define a callback function
Correct Answer:
a. To declare a function as asynchronous and to pause execution until a promise is resolved
Explanation: The async keyword is used to declare a function as asynchronous, and the await keyword is used to pause execution until a promise is resolved.
147. How do you add an element to the end of an array in JavaScript?
c
a. array.addToEnd(element);
b. array.insertLast(element);
c. array.push(element);
d. array.append(element);
Correct Answer:
c. array.push(element);
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
148. What is the purpose of the split method in JavaScript?
vbnet
a. To split a string into an array of substrings based on a specified separator
b. To split an array into multiple arrays
c. To split an object into its properties
d. To split a number into its digits
Correct Answer:
a. To split a string into an array of substrings based on a specified separator
Explanation: The split method is used to divide a string into an array of substrings based on a specified separator.
149. How can you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
150. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
Feel free to ask if you have more questions or if there’s anything else I can assist you with!
151. How do you remove the last element from an array in JavaScript?
c
a. array.removeLast();
b. array.pop();
c. array.deleteLast();
d. array.splice(-1, 1);
Correct Answer:
b. array.pop();
Explanation: The pop method is used to remove the last element from an array in JavaScript.
152. What is the purpose of the localStorage and
sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
153. How can you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
154. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
155. How do you check if a number is an integer in JavaScript?
s
a. Number.isInteger(x);
b. isInteger(x);
c. x.isInteger();
d. typeof x === “integer”;
Correct Answer:
a. Number.isInteger(x);
Explanation: The Number.isInteger method is used to check if a given value is an integer in JavaScript.
156. What is the purpose of the bind method in JavaScript?
a. To create a new array
b. To bind a function to a specific object
c. To add an event listener
d. To concatenate two strings
Correct Answer:
b. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
157. What is the purpose of the async and await keywords in JavaScript?
a. To declare a function as asynchronous and to pause execution until a promise is resolved
b. To create an asynchronous loop
c. To handle exceptions in asynchronous code
d. To define a callback function
Correct Answer:
a. To declare a function as asynchronous and to pause execution until a promise is resolved
Explanation: The async keyword is used to declare a function as asynchronous, and the await keyword is used to pause execution until a promise is resolved.
158. How do you add an element to the end of an array in JavaScript?
c
a. array.addToEnd(element);
b. array.insertLast(element);
c. array.push(element);
d. array.append(element);
Correct Answer:
c. array.push(element);
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
159. What is the purpose of the split method in JavaScript?
vbnet
a. To split a string into an array of substrings based on a specified separator
b. To split an array into multiple arrays
c. To split an object into its properties
d. To split a number into its digits
Correct Answer:
a. To split a string into an array of substrings based on a specified separator
Explanation: The split method is used to divide a string into an array of substrings based on a specified separator.
160. How can you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
161. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
162. How do you remove the last element from an array in JavaScript?
c
a. array.removeLast();
b. array.pop();
c. array.deleteLast();
d. array.splice(-1, 1);
Correct Answer:
b. array.pop();
Explanation: The pop method is used to remove the last element from an array in JavaScript.
163. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
164. How can you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
165. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
166. How do you check if a number is an integer in JavaScript?
s
a. Number.isInteger(x);
b. isInteger(x);
c. x.isInteger();
d. typeof x === “integer”;
Correct Answer:
a. Number.isInteger(x);
Explanation: The Number.isInteger method is used to check if a given value is an integer in JavaScript.
167. What is the purpose of the bind method in JavaScript?
a. To create a new array
b. To bind a function to a specific object
c. To add an event listener
d. To concatenate two strings
Correct Answer:
b. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
168. What is the purpose of the async and await keywords in JavaScript?
a. To declare a function as asynchronous and to pause execution until a promise is resolved
b. To create an asynchronous loop
c. To handle exceptions in asynchronous code
d. To define a callback function
Correct Answer:
a. To declare a function as asynchronous and to pause execution until a promise is resolved
Explanation: The async keyword is used to declare a function as asynchronous, and the await keyword is used to pause execution until a promise is resolved.
169. How do you add an element to the end of an array in JavaScript?
c
a. array.addToEnd(element);
b. array.insertLast(element);
c. array.push(element);
d. array.append(element);
Correct Answer:
c. array.push(element);
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
170. What is the purpose of the split method in JavaScript?
vbnet
a. To split a string into an array of substrings based on a specified separator
b. To split an array into multiple arrays
c. To split an object into its properties
d. To split a number into its digits
Correct Answer:
a. To split a string into an array of substrings based on a specified separator
Explanation: The split method is used to divide a string into an array of substrings based on a specified separator.
171. How can you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
172. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
173. How do you remove the last element from an array in JavaScript?
c
a. array.removeLast();
b. array.pop();
c. array.deleteLast();
d. array.splice(-1, 1);
Correct Answer:
b. array.pop();
Explanation: The pop method is used to remove the last element from an array in JavaScript.
174. What is the purpose of the localStorage and sessionStorage in JavaScript?
a. To store data on the server
b. To store session-specific data
c. To store data with no expiration time
d. To create a temporary storage for the session
Correct Answer:
c. To store data with no expiration time
Explanation: Both localStorage and sessionStorage are used to store key/value pairs with no expiration time, but localStorage persists even after the browser is closed, while sessionStorage is limited to the session.
175. How can you check if an object has a specific property in JavaScript?
less
a. object.hasProperty(“propertyName”);
b. “propertyName” in object;
c. object.propertyExists(“propertyName”);
d. object.check(“propertyName”);
Correct Answer:
b. “propertyName” in object;
Explanation: The in operator is used to check if an object has a specific property in JavaScript.
176. What is the purpose of the reduce method in JavaScript?
a. To reduce the size of an array
b. To sum the elements of an array
c. To reverse the order of elements in an array
d. To filter elements based on a condition
Correct Answer:
b. To sum the elements of an array
Explanation: The reduce method is used to apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
177. How do you check if a number is an integer in JavaScript?
s
a. Number.isInteger(x);
b. isInteger(x);
c. x.isInteger();
d. typeof x === “integer”;
Correct Answer:
a. Number.isInteger(x);
Explanation: The Number.isInteger method is used to check if a given value is an integer in JavaScript.
178. What is the purpose of the bind method in JavaScript?
a. To create a new array
b. To bind a function to a specific object
c. To add an event listener
d. To concatenate two strings
Correct Answer:
b. To bind a function to a specific object
Explanation: The bind method is used to create a new function that, when called, has its this value set to a specific object.
179. What is the purpose of the async and await keywords in JavaScript?
a. To declare a function as asynchronous and to pause execution until a promise is resolved
b. To create an asynchronous loop
c. To handle exceptions in asynchronous code
d. To define a callback function
Correct Answer:
a. To declare a function as asynchronous and to pause execution until a promise is resolved
Explanation: The async keyword is used to declare a function as asynchronous, and the await keyword is used to pause execution until a promise is resolved.
180. How do you add an element to the end of an array in JavaScript?
c
a. array.addToEnd(element);
b. array.insertLast(element);
c. array.push(element);
d. array.append(element);
Correct Answer:
c. array.push(element);
Explanation: The push method is used to add one or more elements to the end of an array in JavaScript.
181. What is the purpose of the split method in JavaScript?
vbnet
a. To split a string into an array of substrings based on a specified separator
b. To split an array into multiple arrays
c. To split an object into its properties
d. To split a number into its digits
Correct Answer:
a. To split a string into an array of substrings based on a specified separator
Explanation: The split method is used to divide a string into an array of substrings based on a specified separator.
182. How can you convert a date to a string in a specific format in JavaScript?
lua
a. date.format(“MM/DD/YYYY”);
b. date.toFormat(“MM/DD/YYYY”);
c. date.toLocaleString(“en-US”, {format: “short”});
d. Intl.DateTimeFormat(“en-US”).format(date);
Correct Answer:
d. Intl.DateTimeFormat(“en-US”).format(date);
Explanation: Using Intl.DateTimeFormat with the format method allows you to convert a date to a string in a specific format.
183. What is the purpose of the Object.create method in JavaScript?
a. To create a new object with the specified prototype object
b. To create a copy of an existing object
c. To merge two objects into one
d. To check if an object has a specific property
Correct Answer:
a. To create a new object with the specified prototype object
Explanation: The Object.create method is used to create a new object with the specified prototype object and properties.
If you have more questions or if there’s anything else I can assist you with, feel free to ask!
184. What is the purpose of the Array.isArray method in JavaScript?
a. To check if a variable is an array
b. To create a new array
c. To remove elements from an array
d. To concatenate two arrays
Correct Answer:
a. To check if a variable is an array
Explanation: The Array.isArray method is used to check if a variable is an array in JavaScript.
185. How do you compare two values for equality without type coercion in JavaScript?
a. x == y;
b. x === y;
c. x.equal(y);
d. x.isEqual(y);
Correct Answer:
b. x === y;
Explanation: The strict equality operator (===) in JavaScript compares two values for equality without type coercion.
186. What is the purpose of the map method in JavaScript?
a. To create a new array with the results of calling a function on every element
b. To reverse the order of elements in an array
c. To filter elements in an array based on a condition
d. To sum the elements of an array
Correct Answer:
a. To create a new array with the results of calling a function on every element
Explanation: The map method is used to create a new array with the results of calling a provided function on every element in the array.
187. How can you convert a string to a number in JavaScript?
s
a. parseInt(string);
b. number(string);
c. toNumber(string);
d. string.toNumber();
Correct Answer:
a. parseInt(string);
Explanation: The parseInt function is commonly used to convert a string to a number in JavaScript.
188. What is the purpose of the Promise object in JavaScript?
a. To handle asynchronous operations and represent a value that might be available now, or in the future, or never
b. To create a new object
c. To check if a value is a promise
d. To define a callback function
Correct Answer:
a. To handle asynchronous operations and represent a value that might be available now, or in the future, or never
Explanation: The Promise object is used to handle asynchronous operations and represents a value that might be available now, or in the future, or never.
189. How do you access the first element of an array in JavaScript?
c
a. array.first();
b. array[0];
c. array.getElement(1);
d. array.head();
Correct Answer:
b. array[0];
Explanation: In JavaScript, array elements are zero-indexed, so you can access the first element using array[0].
190. What is the purpose of the typeof operator in JavaScript?
a. To create a new object
b. To check the type of a variable
c. To concatenate two strings
d. To remove the last element from an array
Correct Answer:
b. To check the type of a variable
Explanation: The typeof operator is used to check the data type of a variable in JavaScript.
191. How do you declare a global variable in JavaScript?
csharp
a. var x = 10;
b. let x = 10;
c. const x = 10;
d. global x = 10;
Correct Answer:
a. var x = 10;
Explanation: In JavaScript, using the var keyword at the top level outside any function creates a global variable.
192. What is the purpose of the Math.floor method in JavaScript?
a. To round a number to the nearest integer
b. To round a number to a specific number of decimal places
c. To generate a random floating-point number
d. To check if a number is an integer
Correct Answer:
a. To round a number to the nearest integer
Explanation: The Math.floor method is used to round a number down to the nearest integer in JavaScript.
193. How do you remove all elements from an array in JavaScript?
c
a. array.removeElements();
b. array.clear();
c. array.removeAll();
d. array.length = 0;
Correct Answer:
d. array.length = 0;
Explanation: Setting the length property of an array to 0 effectively removes all elements from the array in JavaScript.
194. What is the purpose of the typeof operator in JavaScript?
a. To create a new object
b. To check the type of a variable
c. To concatenate two strings
d. To remove the last element from an array
Correct Answer:
b. To check the type of a variable
Explanation: The typeof operator is used to check the data type of a variable in JavaScript.
195. How do you declare a global variable in JavaScript?
csharp
a. var x = 10;
b. let x = 10;
c. const x = 10;
d. global x = 10;
Correct Answer:
a. var x = 10;
Explanation: In JavaScript, using the var keyword at the top level outside any function creates a global variable.