<!DOCTYPE HTML>
<html lang="ja-JP">
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
</body>
<script type="text/javascript">
var num1 = 123456789;
num1 = num1.toString().replace(/([0-9]+?)(?=(?:[0-9]{3})+$)/g , '$1,' );
var num2 = 1.23456789;
num2ary = num2.toString().split(".");
num2ary[0] = num2ary[0].replace(/([0-9]+?)(?=(?:[0-9]{3})+$)/g , '$1,' );
num2ary[1] = "0." + num2ary[1];
num2ary[1] = Math.round(parseFloat(num2ary[1]) * 1000) / 1000;
num2ary[0] = parseFloat(num2ary[0]);
num2ary[1] = parseFloat(num2ary[1]);
num2 = ((num2ary[0] * 1000 + num2ary[1] * 1000) / 1000);
document.getElementsByTagName("body")[0].innerHTML = num1 + "<br>" + num2;
</script>
</html>
<?php
header("Content-type: text/html; charset=utf-8");
echo number_format(123456789) . "<br>";
echo number_format(1.23456789, 3);
?>