<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="css/lx.css">
</head>
<body>

<script>
    //js千分符 三个分成一份
   /* var arr=['11','22','33','44','55','11','22','33'];*/
   var aa = String(10123456789);
   var arr = [];
   var num = aa.length % 3;
   var num2 = 0;
   var tem = '';
   if(num != 0){
var firs = aa.substring(0,num);
       arr.push(firs);
   }
   aa = aa.substring(num);
   for(var i = 0; i < aa.length; i++){
       num2++;
       tem += aa[i];
       if(num2 == 3 && tem){
           arr.push(tem);
           num2 = 0;
           tem = '';
       }
   }

var abc = arr.join(',').replace(/(.*),/,'$1.'); // ,是需要替换的   $1后面的.点 是替换成.

   console.log(abc)


//第二种
var test1 = '1234567890'
function formatCash(str) {
return str.split('').reverse().reduce((prev, next, index) => {
return ((index % 3) ? next : (next + ',')) + prev
    })
}
console.log(formatCash(test1))

</script>
</body>
</html>