80 interview questions on Javascript for developers (2026)

Hard

10 votes2442 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 votes2473 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

Easy

9 votes2462 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

8 votes2538 runs0 comment

What will this code display?

Front-end developer

javascript

function

identity

Jean-marie Cléryat Jan 4, 2022

Hard

7 votes2525 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

7 votes2498 runs

1 comment

Invert a string in Javascript

Front-end developer

arrays

strings

Jean-marie Cléryat Jan 4, 2022

Easy

6 votes2519 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 votes2503 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

5 votes2481 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 votes2471 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 votes2440 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 votes2426 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 votes265 runs1 comment

How to overwrite a property in an object in Javascript

Front-end developer

objects

duplicates

Vincent Cotroat Sep 19, 2022

Hard

4 votes2593 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 votes2556 runs

2 comments

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 votes2537 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

4 votes2506 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 votes2524 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 votes2511 runs3 comments

Write a function that returns a string 'Haha!'

Front-end developer

functions

return

Jean-marie Cléryat Jan 4, 2022

Hard

3 votes2509 runs0 comment

Which of the following equality(s) returns`true`?

Front-end developer

javascript

NaN

Jean-marie Cléryat Jan 4, 2022

80 interview questions on Javascriptfor developers (2026)

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'

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

What will this code display?

Identify the reasons why this code will not work correctly:

Invert a string 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?

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)?

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

How to call a function inside a function in Javascript

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

Write a function that returns a string 'Haha!'

Which of the following equality(s) returns`true`?

80 interview questions on Javascriptfor developers (2026)

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'

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

What will this code display?

Identify the reasons why this code will not work correctly:

Invert a string 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?

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)?

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

How to call a function inside a function in Javascript

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

Write a function that returns a string 'Haha!'

Which of the following equality(s) returns`true`?

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

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