function reduce(arr, callBack ,initVal){

            if(!Array.isArray(arr) || !arr.length || typeof callBack != 'function') return [];

            let hasInitVal = initVal !== 'undefined';

            let val = hasInitVal ? initVal : arr[0];

            for(let i = 0, len = arr.length; i<len; i++){

                val = callBack(value, arr[i], i, arr);

            }

            return val

        }