JavaScript: Flatten a given array up to the specified depth

JavaScript fundamental (ES6 Syntax): Exercise-234 with Solution

Flatten Array to Depth

Write a JavaScript program to flatten a given array to the specified depth.

• Use recursion, decrementing depth by 1 for each level of depth.
• Use Array.prototype.reduce() and Array.prototype.concat() to merge elements or arrays.
• Base case, for depth equal to 1 stops recursion.
• Write a JavaScript program to flatten a given array to the specified depth.

Sample Solution:

JavaScript Code:

// Define a function 'flatten' that flattens nested arrays up to a specified depth
const flatten = (arr, depth = 1) =>
  arr.reduce((a, v) => 
    a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);

// Test the 'flatten' function with sample arrays
console.log(flatten([1, [2], 3, 4])); // Output: [1, 2, 3, 4]
console.log(flatten([1, [2, [3, [4, 5], 6], 7], 8], 2)); // Output: [1, 2, 3, [4, 5], 6, 7, 8]

Output:

[1,2,3,4]
[1,2,3,[4,5],6,7,8]

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-234-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that flattens an array to a specified depth using recursion.
• Write a JavaScript function that takes a nested array and returns a new array flattened to the given level.
• Write a JavaScript program that implements a custom flatten function with a depth parameter, without using flat().
• Write a JavaScript function that reduces nested arrays to a one-dimensional array up to a specified depth.

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