<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Integers</title>
</head>
<body>
<script type="text/javascript">
Number.prototype.fixIt = function(){
var numbers = this.toFixed(2).split('.')
var integer = numbers[0]
var decimal = numbers[1]
var numbers = integer.split('')
var saida = ''
for (i=numbers.length-1;i>=0;i--) {
if (!(i%3)) {
saida = '.' + saida
}
saida = numbers[i] + saida
}
// Removendo o ponto extra que pode ficar
saida = saida.replace(/\.$/, '')
return saida + ',' + decimal
}
document.write((1234.500).fixIt())
</script>
</body>
</html>