JavaScriptで数字3桁ごとにコンマを打つ

● JavaScriptで数字3桁ごとにコンマを打つ

<html><body>
<script>
var data1=123456789;
alert(data1);

data2=comma(data1);
alert(data2);

function comma(num) {
    return num.toString().replace( /([0-9]+?)(?=(?:[0-9]{3})+$)/g , '$1,' );
} 
</script>
</body>
</html>