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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.

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80 questions
Easy
10 votes2488 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
10 votes2466 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 votes2500 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
8 votes2567 runs0 comment

What will this code display?

Front-end developer
javascript
function
identity
Jean-marie Cléryat Jan 4, 2022
Hard
7 votes2551 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 votes2525 runs
1 comment

Invert a string in Javascript

Front-end developer
arrays
strings
Jean-marie Cléryat Jan 4, 2022
Easy
6 votes2548 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
6 votes267 runs1 comment

How to overwrite a property in an object in Javascript

Front-end developer
objects
duplicates
Anonymous authorat Sep 19, 2022
Hard
5 votes2528 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 votes2510 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 votes2497 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 votes2463 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 votes2455 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
4 votes2614 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 votes2583 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 votes2564 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 votes2535 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 votes2547 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 votes2540 runs3 comments

Write a function that returns a string 'Haha!'

Front-end developer
functions
return
Jean-marie Cléryat Jan 4, 2022
Hard
3 votes2540 runs0 comment

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

Front-end developer
javascript
NaN
Jean-marie Cléryat Jan 4, 2022
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