1.jpg

    代码如下:

    1. Array.prototype.filter = function(callbackfn, thisArg) {
    2.   // 处理数组类型异常
    3.   if (this === null || this === undefined) {
    4.     throw new TypeError("Cannot read property 'filter' of null or undefined");
    5.   }
    6.   // 处理回调类型异常
    7.   if (Object.prototype.toString.call(callbackfn) != "[object Function]") {
    8.     throw new TypeError(callbackfn + ' is not a function')
    9.   }
    10.   let O = Object(this);
    11.   let len = O.length >>> 0;
    12.   let resLen = 0;
    13.   let res = [];
    14.   for(let i = 0; i < len; i++) {
    15.     if (i in O) {
    16.       let element = O[i];
    17.       if (callbackfn.call(thisArg, O[i], i, O)) {
    18.         res[resLen++] = element;
    19.       }
    20.     }
    21.   }
    22.   return res;
    23. }

    MDN上所有测试用例亲测通过。

    参考:

    V8数组部分源码第1025行

    MDN中filter文档

    三元博客