复制
1Array.prototype.forEach = function(callback, thisArg) {
2  if (this == null) {
3    throw new TypeError('this is null or not defined');
4  }
5  if (typeof callback !== "function") {
6    throw new TypeError(callback + ' is not a function');
7  }
8  const O = Object(this);
9  const len = O.length >>> 0;
10  let k = 0;
11  while (k < len) {
12    if (k in O) {
13      callback.call(thisArg, O[k], k, O);
14    }
15    k++;
16  }
17}