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