题解 | #Array.map#
Array.map
http://www.nowcoder.com/practice/8300c998180c4ebbbd2a5aaeb7fbc77c
Array.prototype._map = function (fn){
if(typeof fn !== "function") return ;
let arr = [];
for(let i = 0;i<this.length;i++){
arr.push(fn(this[i],i,this))
}
return arr;
}