JavaScript: Deep flatten an array

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

Deep Flatten Array

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 
// Define a function 'deepFlatten' to recursively flatten nested arrays
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));

// Call the 'deepFlatten' function with a nested array and log the flattened result
console.log(deepFlatten([1, [2], [[3], 4], 5]));

Output:

[1,2,3,4,5]

Flowchart:

Live Demo:

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

For more Practice: Solve these Related Problems:

• Write a JavaScript program that recursively flattens a nested array to produce a one-dimensional array.
• Write a JavaScript function that uses recursion to flatten arrays of arbitrary depth.
• Write a JavaScript program that deep flattens an array without using Array.flat() or similar built-in methods.
• Write a JavaScript function that checks each element for array-ness and concatenates them into a flat array.

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