一个数组的和

function foo (...args) {
            return args.reduce(function (previousValue, currentValue) {
                // console.log(previousValue, currentValue)
                return previousValue += currentValue;
            })
        }

        console.log(foo(1, 32, 34, 5, 6))

 function sum () {
            var result = 0;

            for(var i = 0, len = arguments.length; i < len; i++) {
                result += arguments[i]
            }

            return result;
        }

        console.log(sum(1, 2, 3 , 4, 5))