JS: Array.prototype.flat

By Xah Lee. Date: . Last updated: .

(new in ECMAScript 2019)

xArray.flat()
flatten nested array 1 level. Return a new array.
xArray.flat(n)
flatten n times. 
const xx = [0, [1, [2, [3, [4]]]]];

console.assert(
 JSON.stringify(xx.flat()) ===
  "[0,1,[2,[3,[4]]]]",
);

console.assert(
 JSON.stringify(xx.flat(1)) ===
  "[0,1,[2,[3,[4]]]]",
);

console.assert(
 JSON.stringify(xx.flat(2)) ===
  "[0,1,2,[3,[4]]]",
);

console.assert(
 JSON.stringify(xx.flat(3)) ===
  "[0,1,2,3,[4]]",
);