题解 | #Array.reduce#
Array.reduce
http://www.nowcoder.com/practice/213d0ef21cb841de8cf69fcc5ea60eb6
Array.prototype._reduce = function (fn){
if(typeof fn !== "function") return ;
let num = 0;
for(let i = 0;i<this.length;i++){
num = fn(num,this[i],i,this)
}
return num;
}