``` // for循环实现 Array.prototype.myMap = function () { var arr = this var [fn, thisValue] = Array.prototype.slice.call(arguments) var result = [] for (var i = 0; i < arr.length; i++) { result.push(fn.call(thisValue, arr[i], i, arr)) } return result } var arr0 = [1, 2, 3] console.log(arr0.myMap(v => v + 1)) ``` ``` // forEach实现(reduce类似) Array.prototype.myMap = function (fn, thisValue) { var result = [] this.forEach((v, i, arr) => { result.push(fn.call(thisValue, v, i, arr)) }) return result } var arr0 = [1, 2, 3] console.log(arr0.myMap(v => v + 1)) ```