80 interview questions on Javascript for developers (2025)

Hard

9 votes2160 runs3 comments

Write a Javascript code that prints the indexes of an array.

Front-end developer

array

for loop

Jean-marie Cléryat Nov 8, 2023

Hard

8 votes2191 runs1 comment

Which of the following equality(s) are true? 0 == '', 'f' + 1 == 'f1'

Front-end developer

javascript

equality

Jean-marie Cléryat Jan 4, 2022

Hard

7 votes2208 runs0 comment

Invert a string in Javascript

Front-end developer

arrays

strings

Jean-marie Cléryat Jan 4, 2022

Easy

7 votes2199 runs0 comment

Which of the following is the most optimized method for creating a literal object?

Front-end developer

javascript

objects

Jean-marie Cléryat Jan 4, 2022

Hard

6 votes2261 runs0 comment

What will this code display?

Front-end developer

javascript

function

identity

Jean-marie Cléryat Jan 4, 2022

Hard

5 votes2202 runs1 comment

How to call a function inside a function in Javascript

Front-end developer

functions

objects

Jean-marie Cléryat Jan 4, 2022

Hard

5 votes238 runs1 comment

How to overwrite a property in an object in Javascript

Front-end developer

objects

duplicates

Vincent Cotroat Sep 19, 2022

Easy

4 votes2243 runs2 comments

Write a Javascript code that displays the contents of the table : Peter, Paul, Jacques, and the length of the table.

Front-end developer

arrays

console.log

push

Jean-marie Cléryat Jan 4, 2022

Hard

4 votes2233 runs1 comment

What is the value of `obj.hello` after executing these few lines of code?

Front-end developer

objects

arrays

strings

Jean-marie Cléryat Oct 20, 2023

Hard

4 votes2232 runs0 comment

Identify the reasons why this code will not work correctly:

Front-end developer

javascript

html

form

Jean-marie Cléryat Jan 4, 2022

Hard

4 votes2197 runs0 comment

Which statement(s) is/are true about the `localStorage` API?

Front-end developer

javascript

api

storage

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2268 runs0 comment

Which of the following features are part of version ES2015(formerly ES6)?

Front-end developer

es6

promises

arrow functions

Jean-marie Cléryat Jan 4, 2022

Medium

3 votes2239 runs1 comment

How to make an AJAX call to an external domain that makes public data available.

Front-end developer

ajax

authentication

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2234 runs0 comment

Explain the difference between `proto` and `prototype` in Javascript

Front-end developer

prototype

constructor

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2187 runs0 comment

Explain the 2 phases of event propagation in the DOM.

Front-end developer

event

event propagation

Jean-marie Cléryat Jan 4, 2022

Medium

3 votes2181 runs0 comment

Write a Javascript code that will display the letters A, B, C, D in the console.

Front-end developer

array

function

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2166 runs0 comment

What will be the first thing that the following code displays?

Front-end developer

inheritance

prototype

constructor

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2158 runs0 comment

Use map, filter and reduce to calculate the sum of the marks of students with a mark greater than 10.

Front-end developer

array

map

filter

reduce

Jean-marie Cléryat Jan 4, 2022

Medium

3 votes276 runs1 comment

Print the value of the variable name and age in the function sayHi()

Front-end developer

functions

variables

Vincent Cotroat Sep 19, 2022

Medium

3 votes224 runs0 comment

Compare two numbers in Javascript

Front-end developer

equality

comparison

type

Vincent Cotroat Sep 19, 2022

80 interview questions on Javascriptfor developers (2025)

Test your technical skills before an interview of Javascript with 80 corrected questions. Beginner, Intermediate or Expert level.

Write a Javascript code that prints the indexes of an array.

Which of the following equality(s) are true? 0 == '', 'f' + 1 == 'f1'

Invert a string in Javascript

Which of the following is the most optimized method for creating a literal object?

What will this code display?

How to call a function inside a function in Javascript

How to overwrite a property in an object in Javascript

Write a Javascript code that displays the contents of the table : Peter, Paul, Jacques, and the length of the table.

What is the value of `obj.hello` after executing these few lines of code?

Identify the reasons why this code will not work correctly:

Which statement(s) is/are true about the `localStorage` API?

Which of the following features are part of version ES2015(formerly ES6)?

How to make an AJAX call to an external domain that makes public data available.

Explain the difference between `proto` and `prototype` in Javascript

Explain the 2 phases of event propagation in the DOM.

Write a Javascript code that will display the letters A, B, C, D in the console.

What will be the first thing that the following code displays?

Use map, filter and reduce to calculate the sum of the marks of students with a mark greater than 10.

Print the value of the variable name and age in the function sayHi()

Compare two numbers in Javascript

80 interview questions on Javascriptfor developers (2025)

Test your technical skills before an interview of Javascript with 80 corrected questions. Beginner, Intermediate or Expert level.

Write a Javascript code that prints the indexes of an array.

Which of the following equality(s) are true? 0 == '', 'f' + 1 == 'f1'

Invert a string in Javascript

Which of the following is the **most optimized** method for creating a literal object?

What will this code display?

How to call a function inside a function in Javascript

How to overwrite a property in an object in Javascript

Write a Javascript code that displays the contents of the table : Peter, Paul, Jacques, and the length of the table.

What is the value of `obj.hello` after executing these few lines of code?

Identify the reasons why this code will not work correctly:

Which statement(s) is/are true about the `localStorage` API?

Which of the following features are part of version ES2015(formerly ES6)?

How to make an AJAX call to an external domain that makes public data available.

Explain the difference between `__proto__` and `prototype` in Javascript

Explain the 2 phases of event propagation in the DOM.

Write a Javascript code that will display the letters A, B, C, D in the console.

What will be the first thing that the following code displays?

Use map, filter and reduce to calculate the sum of the marks of students with a mark greater than 10.

Print the value of the variable name and age in the function sayHi()

Compare two numbers in Javascript

Which of the following is the most optimized method for creating a literal object?

Explain the difference between `proto` and `prototype` in Javascript