JavaScript: Flatten a given array up to the specified depth
JavaScript fundamental (ES6 Syntax): Exercise-234 with Solution
Write a JavaScript program to flatten a given array up 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.
- Omit the second argument, depth, to flatten only to a depth of 1 (single flatten).
Sample Solution:
JavaScript Code:
//#Source https://bit.ly/2neWfJ2
const flatten = (arr, depth = 1) =>
arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);
console.log(flatten([1, [2], 3, 4]));
console.log(flatten([1, [2, [3, [4, 5], 6], 7], 8], 2));
Sample 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.
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Previous: Write a JavaScript program to flatten an object with the paths for keys.
Next: Write a JavaScript program to get the last key that satisfies the provided testing function, otherwise undefined is returned.
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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"; console.log(string.includes(substring));
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
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