实现数组的push、filter、map方法 1、实现push方法let arr = []; Array.prototype.push = function() { for( let i = 0 ; i < arguments.length ; i++){ this[this.length] = arguments[i] ; } return this.length; }2、实现filter方法Array.prototype.filter = function(fn) { if (typeof fn !== "function") { throw Error('请传入一个函数'); } const res = []; for (let i = 0, len = this.length; i < len; i++) { fn(this[i]) && res.push(this[i]); } return res; }3、实现map方法Array.prototype.map = function(fn) { if (typeof fn !== "function") { throw Error('参数是函数'); } const res = []; for (let i = 0, len = this.length; i < len; i++) { res.push(fn(this[i])); } return res; }