Array flat的实现

if (!Array.prototype.flat) {
    Array.prototype.flat = function (num = 1) {
        if (!Number(num) || Number(num) < 0) {
            return this;
        }
        var arr = []
        this.forEach((item) => {
            if (Array.isArray(item)) {
                arr = arr.concat(item.flat(--num))
            } else {
                arr.push(item)
            }
        })
        return arr
    }
}

测试用例

const arr = [1, [2, [3, 'a', [4]]]]

console.log(arr.flat('dsdsadf'));  // [1, [2, [3, 'a', [4]]]]
console.log(arr.flat(-32)); // [1, [2, [3, 'a', [4]]]]
console.log(arr.flat(0));   // [1, [2, [3, 'a', [4]]]]
console.log(arr.flat('1'));   // [1, 2, [3, 'a', [4]]]
console.log(arr.flat('2'));    // [1, 2, 3, 'a', [4]]
console.log(arr.flat(3));       // [1, 2, 3, 'a', 4]
console.log(arr.flat(Infinity));     // [1, 2, 3, 'a', 4]
console.log(arr.flat('Infinity'));   // [1, 2, 3, 'a', 4]