JavaScript: Deep flatten an array

JavaScript fundamental (ES6 Syntax): Exercise-248 with Solution

Write a JavaScript program to deep flatten an array.

  • Use recursion.
  • Use Array.prototype.concat() with an empty array ([]) and the spread operator (...) to flatten an array.
  • Recursively flatten each element that is an array.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
console.log(deepFlatten([1, [2], [[3], 4], 5]));

Sample Output:



flowchart: Deep flatten an array.

Live Demo:

See the Pen javascript-basic-exercise-248-1 by w3resource (@w3resource) on CodePen.

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JavaScript: Tips of the Day

How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes:

const string = "foo";
const substring = "oo";


includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:

var string = "foo";
var substring = "oo";

console.log(string.indexOf(substring) !== -1);

Ref: https://bit.ly/3fFFgZv