JavaScript

Which method is used to convert JSON data to a JavaScript object? a) JSON.parse() b) JSON.stringify() c) Object.assign() d) Array.from() Answer: a) JSON.parse() Explanation: The JSON.parse() method is used to convert a JSON string into a JavaScript object. This is commonly used when receiving JSON data from an API or another external source. Reference: JavaScript […]

What is the purpose of the Array.filter() method in JavaScript? a) To create a new array with elements that pass a test b) To remove elements from the original array c) To apply a function to every element of an array d) To sort the elements of an array Answer: a) To create a new

What is the output of the following code: console.log(typeof NaN);? a) "undefined" b) "number" c) "object" d) "NaN" Answer: b) "number" Explanation: In JavaScript, NaN stands for “Not-a-Number”, but it is still considered a numeric value. When checking the type of NaN using typeof, the result is "number". Reference: JavaScript MCQ (Multiple-Choice Questions)

Which of the following will correctly check if a variable is an array in JavaScript? a) Array.isArray(variable) b) typeof variable === 'array' c) variable.isArray() d) variable instanceof Object Answer: a) Array.isArray(variable) Explanation: The most reliable way to check if a variable is an array in JavaScript is by using Array.isArray(variable). This method returns true if

What is the purpose of Array.map() in JavaScript? a) To create a new array by transforming every element in an array b) To filter out elements from an array c) To find the index of an element in an array d) To modify the original array Answer: a) To create a new array by transforming

What will the console.log(0.1 + 0.2 === 0.3) statement output? a) true b) false c) undefined d) NaN Answer: b) false Explanation: In JavaScript, the expression 0.1 + 0.2 === 0.3 evaluates to false due to floating-point precision issues. JavaScript uses floating-point arithmetic, which cannot precisely represent some decimal numbers, leading to small errors in

How do you remove duplicates from an array in JavaScript? a) Using Set() b) Using Array.filter() c) Using Array.reduce() d) Using Array.map() Answer: a) Using Set() Explanation: One of the easiest ways to remove duplicates from an array in JavaScript is by using Set(). A Set object stores unique values, and you can convert the

What is the purpose of JSON.stringify() in JavaScript? a) To convert a JavaScript object into a JSON string b) To convert a JSON string into a JavaScript object c) To sort the properties of a JavaScript object d) To clone a JavaScript object Answer: a) To convert a JavaScript object into a JSON string Explanation:

What is the difference between let and var in JavaScript? a) let is block-scoped, while var is function-scoped b) var is block-scoped, while let is function-scoped c) let can be redeclared, while var cannot d) There is no difference Answer: a) let is block-scoped, while var is function-scoped Explanation: The key difference between let and

What is the purpose of the reduce() method in JavaScript arrays? a) To reduce the length of an array b) To apply a function to each element and accumulate the result c) To remove duplicates from an array d) To remove elements from an array Answer: b) To apply a function to each element and

Which of the following methods is used to find the index of an element in an array in JavaScript? a) indexOf() b) findIndex() c) find() d) search() Answer: a) indexOf() Explanation: The indexOf() method returns the first index at which a given element can be found in an array, or -1 if the element is

What will the console.log([] + []) statement output? a) "" b) [] c) undefined d) NaN Answer: a) "" Explanation: In JavaScript, when two empty arrays are added together, the result is an empty string "". This is because JavaScript first converts the arrays to strings, and the string representation of an empty array is

How can you convert a string to a number in JavaScript? a) parseFloat() b) parseInt() c) Number() d) All of the above Answer: d) All of the above Explanation: In JavaScript, you can convert a string to a number using parseFloat(), parseInt(), or Number(). Each has its specific use cases. parseInt() converts a string to

Which of the following is true about the this keyword in JavaScript arrow functions? a) this refers to the global object b) this is lexically bound c) this refers to the parent function’s scope d) this is dynamically bound Answer: b) this is lexically bound Explanation: In arrow functions, the this keyword is lexically bound,

What will the console.log(NaN === NaN) statement output? a) true b) false c) undefined d) NaN Answer: b) false Explanation: In JavaScript, NaN (Not-a-Number) is a special value that represents an undefined or unrepresentable number. When comparing NaN with itself using ===, the result is false. This is because NaN is not considered equal to

Which of the following is the correct way to declare an arrow function in JavaScript? a) let myFunc = () => { … } b) let myFunc => () { … } c) let myFunc = () { => … } d) let myFunc => { … } Answer: a) let myFunc = () =>

What is the output of the following code: console.log([] == false);? a) true b) false c) undefined d) NaN Answer: a) true Explanation: In JavaScript, an empty array [] is loosely equal (==) to false due to type coercion. When using ==, both operands are converted to the same type before comparison, resulting in true

Which of the following is true about const in JavaScript? a) A variable declared with const cannot be reassigned b) A variable declared with const is block-scoped c) The value of a const variable can be an object or array d) All of the above Answer: d) All of the above Explanation: Variables declared with

What is the purpose of the setTimeout() function in JavaScript? a) To delay the execution of a function by a specified amount of time b) To execute a function repeatedly after a set interval c) To set a function to run immediately d) To terminate the execution of a function Answer: a) To delay the

What will the console.log(null == undefined) statement output? a) true b) false c) undefined d) NaN Answer: a) true Explanation: In JavaScript, null and undefined are loosely equal (==), meaning they are treated as the same value in non-strict comparison, so null == undefined returns true. However, they are not strictly equal (===), as their

What is a callback function in JavaScript? a) A function passed as an argument to another function b) A function that returns multiple values c) A function that runs in the background d) A function that loops indefinitely Answer: a) A function passed as an argument to another function Explanation: A callback function is a

Which of the following statements will result in true when using the strict equality operator (===)? a) 5 === "5" b) null === undefined c) true === 1 d) 5 === 5 Answer: d) 5 === 5 Explanation: The strict equality operator (===) compares both the value and type of two variables. The statement 5

What will the Array.unshift() method do? a) Add one or more elements to the beginning of an array b) Remove the first element of an array c) Add one or more elements to the end of an array d) Sort the elements of an array Answer: a) Add one or more elements to the beginning

Which of the following methods is used to remove the last element from an array in JavaScript? a) pop() b) shift() c) splice() d) remove() Answer: a) pop() Explanation: The pop() method is used to remove the last element from an array in JavaScript. It modifies the original array and returns the removed element. Example:

What does the typeof operator return for an undefined variable? a) “undefined” b) “null” c) “object” d) “number” Answer: a) “undefined” Explanation: The typeof operator in JavaScript returns the string “undefined” when used on a variable that has not been assigned a value. This is different from null, which is an object. For example: let