算法打卡day4——手写reduce

Array.prototype.myReduce = function(cb, initial_value){
    const arr = this;
    const startIndex = (initial_value || initial_value === 0) ? 0 : 1
    const total =  (initial_value || initial_value === 0) ? initial_value : arr[0]
    for(let i = startIndex; i < arr.length; i ++){
        total = cb(total, arr[i], i, arr)
    }
    return total
}