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flatten

TS JS Deno

Flattens an 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).

typescript
const flatten = (arr: any[], depth = 1): any[] => {
if (typeof Array.prototype.flat !== "undefined") return arr.flat(depth);
return arr.reduce(
(a, v) =>
a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v),
[]
);
};
typescript
flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]