js给多位数字加上千分位分割符号，

const science = (num) => { 
    var str = '';
    if(typeof num == 'number') {
        str = num.toString();
    } else if(typeof num == 'string'){
        str = num;
    } else {
        return num;
    }
    var re = /(?=(?!\b)(\d{3})+$)/g; 
    return str.replace(re, ','); 
 }