80 interview questions on Javascript for developers (2025)

Hard

9 votes2197 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 votes2237 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 votes2251 runs0 comment

Invert a string in Javascript

Front-end developer

arrays

strings

Jean-marie Cléryat Jan 4, 2022

Easy

7 votes2247 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 votes2314 runs0 comment

What will this code display?

Front-end developer

javascript

function

identity

Jean-marie Cléryat Jan 4, 2022

Hard

5 votes2251 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 votes243 runs1 comment

How to overwrite a property in an object in Javascript

Front-end developer

objects

duplicates

Vincent Cotroat Sep 19, 2022

Easy

4 votes2290 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 votes2276 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 votes2269 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 votes2250 runs0 comment

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

Front-end developer

javascript

api

storage

Jean-marie Cléryat Jan 4, 2022

Medium

4 votes2223 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

4 votes2210 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 votes2352 runs1 comment

Which of the following objects does not exist in modern JavaScript?

Front-end developer

objects

javascript

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2309 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 votes2292 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 votes2284 runs

1 comment

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

Front-end developer

prototype

constructor

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2230 runs0 comment

Explain the 2 phases of event propagation in the DOM.

Front-end developer

event

event propagation

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2206 runs1 comment

Write a module in Javascript

Front-end developer

module

pattern

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2204 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

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.

Identify the reasons why this code will not work correctly:

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

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

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?

Which of the following objects does not exist in modern JavaScript?

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 module in Javascript

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

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.

Identify the reasons why this code will not work correctly:

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

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

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?

Which of the following objects does not exist in modern JavaScript?

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 module in Javascript

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

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

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