```js Array.prototype.getLevel = function () { let max = 1 for (const a of this) { if (a instanceof Array) { const depth = a.getLevel() + 1 if (max < depth) max = depth } } return max }; const a1 = [1, 2, [1], [1, [2, [3]]]]; console.log(a1.getLevel()); //4 ```