题解 | #分隔符#

function _comma(number) {
        // 补全代码
        if (number < 0) return number.toString();
        number = Math.floor(number);
        const s = number.toString();
        const arr = s.split('').reverse();
        return arr.reduce((pre,val,index) => {
            if (index%3===0) {
                if (pre) {
                    val + ',' + pre
                }else {
                    return val
                }
            }else {
                return val+pre
            }
        },'')
    }