.flat(depth)

Flattens a nested array by the specified depth.

Examples:

let nestedArray = [1, [2, [3, [4, 5]]]];
let flatArray = nestedArray.flat();
console.log(flatArray); // [1, 2, [3, [4, 5]]]

let deeplyNestedArray = [1, [2, [3, [4, 5]]]];
let flatDeepArray = deeplyNestedArray.flat(2);
console.log(flatDeepArray); // [1, 2, 3, [4, 5]]