<! DOCTYPEhtml>      
<html lang="en">      
<head>      
    <meta charset="UTF-8">      
    <title>Add a comma thousandth every three digits to a number</title>    
    <style type="text/css">
    </style>     
</head>      
<body>
	<script type="text/javascript">
 	function farmat(mun) {
        if (mun === null) return;
        var m = parseInt(mun).toString();
        var len = m.length;
        if (len <= 3) return m;
        var n = len % 3;
        if (n > 0) {
            return m.slice(0,n)+","+m.slice(n,len).match(/\d{3}/g).join(",")}else {
            return m.slice(n,len).match(/\d{3}/g).join(",")}}var a =farmat(1000000)
    console.log(a);	  //1,000,000
	</script>
</body>      
</html> 
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