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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.

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80 questions
Hard
10 votes2280 runs3 comments
Hard
8 votes2316 runs
2 comments
Hard
7 votes2388 runs0 comment

What will this code display?

Front-end developer
javascript
function
identity
Jean-marie Cléryat Jan 4, 2022
Hard
7 votes2336 runs
1 comment

Invert a string in Javascript

Front-end developer
arrays
strings
Jean-marie Cléryat Jan 4, 2022
Easy
7 votes2309 runs0 comment
Hard
5 votes2358 runs0 comment
Medium
5 votes2294 runs0 comment
Hard
5 votes2286 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 votes249 runs1 comment
Hard
4 votes2438 runs1 comment
Hard
4 votes2346 runs1 comment
Hard
4 votes2333 runs
2 comments
Hard
4 votes2320 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 votes2398 runs
1 comment
Hard
3 votes2374 runs1 comment
Hard
3 votes2361 runs
1 comment
Hard
3 votes2360 runs3 comments

Write a function that returns a string 'Haha!'

Front-end developer
functions
return
Jean-marie Cléryat Jan 4, 2022
Hard
3 votes2343 runs
1 comment
Hard
3 votes2302 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