80 interview questions on Javascript for developers (2025)

Hard

10 votes2354 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

9 votes2390 runs

2 comments

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 votes2463 runs0 comment

What will this code display?

Front-end developer

javascript

function

identity

Jean-marie Cléryat Jan 4, 2022

Hard

7 votes2413 runs

1 comment

Invert a string in Javascript

Front-end developer

arrays

strings

Jean-marie Cléryat Jan 4, 2022

Easy

7 votes2382 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 votes2440 runs0 comment

Identify the reasons why this code will not work correctly:

Front-end developer

javascript

html

form

Jean-marie Cléryat Jan 4, 2022

Easy

5 votes2436 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

5 votes2396 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

5 votes2382 runs

2 comments

Which of the following code will log the message 'baz'?

Front-end developer

javascript

function

prototype

Jean-marie Cléryat Jan 4, 2022

Medium

5 votes2367 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

5 votes2357 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

5 votes253 runs1 comment

How to overwrite a property in an object in Javascript

Front-end developer

objects

duplicates

Vincent Cotroat Sep 19, 2022

Hard

4 votes2514 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

4 votes2476 runs

1 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

Hard

4 votes2425 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 votes2415 runs

2 comments

How to call a function inside a function in Javascript

Front-end developer

functions

objects

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2453 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 votes2447 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 votes2433 runs3 comments

Write a function that returns a string 'Haha!'

Front-end developer

functions

return

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2418 runs

1 comment

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

Front-end developer

javascript

api

storage

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'

What will this code display?

Invert a string in Javascript

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

Identify the reasons why this code will not work correctly:

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

Explain the 2 phases of event propagation in the DOM.

Which of the following code will log the message 'baz'?

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?

How to overwrite a property in an object in Javascript

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

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

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

How to call a function inside a function in Javascript

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

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

Write a function that returns a string 'Haha!'

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

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'

What will this code display?

Invert a string in Javascript

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

Identify the reasons why this code will not work correctly:

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

Explain the 2 phases of event propagation in the DOM.

Which of the following code will log the message 'baz'?

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?

How to overwrite a property in an object in Javascript

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

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

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

How to call a function inside a function in Javascript

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

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

Write a function that returns a string 'Haha!'

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

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

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