How to FLATTEN an array in JavaScript? (4 ways in under 14 mins!)

Publié le: 17 janvier 2026
sur la chaîne: Cooking The Code
105
12

Timestamps:
0:04 - What does Flattening mean?
0:40 - flat()
02:37 - loop + recursion
06:33 - Recap of solution
07:27 - reduce + recursion
10:09 - Recap of solution
11:02 - No Recursion
13:15 - Outro

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Ever wondered how to flatten a nested array in JavaScript?
This is one of the most common JavaScript interview questions, and in this video, I break it down step by step using 4 different approaches, from beginner-friendly to interview-level solutions.

You’ll already know what this video is about from the title — so yeah, let’s get started 😄
🔍 What you’ll learn in this video:

What flattening an array actually means

How to flatten deeply nested arrays

4 different ways to solve the same problem

Which approach to use in real projects vs interviews

Pros & cons of each solution

This video is perfect if you’re:

Preparing for JavaScript interviews

Learning DSA in JavaScript

Wanting to write cleaner, more optimized JS code


Flattening an array is one of the most asked JavaScript interview questions, and if you only know one solution, you’re already limiting yourself.

In this video, you’ll learn how to flatten a nested array in JavaScript using 4 different approaches, explained line by line — from beginner-friendly solutions to interview-ready and senior-level techniques.

You’ll already know what this video is about from the title — so yeah, let’s get started.

🔍 What you’ll learn in this JavaScript tutorial:

What flattening an array means in JavaScript

How to flatten deeply nested arrays

Flatten arrays using built-in methods

Flatten arrays using recursion

Flatten arrays using reduce()

Flatten arrays without recursion

Which solution is best for JavaScript interviews

This video is ideal if you are:

Preparing for JavaScript interviews

Learning Data Structures and Algorithms in JavaScript

A frontend developer or full-stack developer

Looking to improve problem-solving skills in JavaScript

Convert this nested array:

[1, [2, [3, 4]], 5]


Into a single-level array:

[1, 2, 3, 4, 5]


No matter how deep the nesting is.


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