This code worked for me:

<p id="calculation"></p>

<script>
    function numberWithCommas(x) {
        var parts = x.toString().split(".");
        parts[0]=parts[0].replace(/\B(?=(\d{3})+(?!\d))/g,".");
        return parts.join(",");
        }

        var calculation = 1231739216.34367;

        document.getElementById("calculation").innerHTML = numberWithCommas((calculation).toFixed(2))
</script>

This code will:

1. Round (for business) to two digits after dezimal.
2. Change the decimal dot to comma.
3. Set a dot every third digit before decimal.

ECMAScript Internationalization API has a number formatting funciton. Intl.NumberFormat()

You can use it like this with pure javascript:

var calculation = document.getElementById('money').value;

//1st way
var moneyFormatter  = new Intl.NumberFormat();
document.getElementById('formattedMoney').innerText = moneyFormatter.format(calculation);

// 2nd way, using currency
var moneyFormatter2 = new Intl.NumberFormat('en-US', {
  style: 'currency',
  currency: 'USD',
  minimumFractionDigits: 2
});

document.getElementById('formattedMoney2').innerText = moneyFormatter2.format(calculation);

<label>Calculation:</label> <input type="text" value="123456789.25" name="money" id="money" />

<ul>
  <li>Number Format: <b><span id="formattedMoney"></span></b><br/><br/></li>
  <li>Currency Format: <b><span id="formattedMoney2"></span><b/></li>
</ul>

IE11, Firefox and Chrome support it, but i am not sure about other browsers.

http://www.ecma-international.org/ecma-402/1.0/#sec-11.1.2

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NumberFormat

You should use an additional String#replace with a regular expression (to match digits in groups of threes before the ,) and a replacement function (to prepend . to each match).

Your Updated Code:

var calculation = $('select[name=somevalue1] option:selected').data('calc') - ($('select[name=somevalue1] option:selected').data('calc') / 100 * $('select[name=somevalue2] option:selected').data('calc')) - ($('select[name=somevalue1] option:selected').data('calc') - ($('select[name=somevalue1] option:selected').data('calc') / 100 * $('select[name=somevalue2] option:selected').data('calc'))) / 100 * $('select[name=somevalue3] option:selected').data('calc')

function format(n) {
  return n.toFixed(2).replace('.', ',').replace(/\d{3}(?=(\d{3})*,)/g, function(s) {
    return '.' + s
  })
}

$('#calculation').text(format(calculation))

Demo Implementation:

var calculations = [
  1234.56,
  1234567.89,
  1234,
  .12
]

function format (n) {
  return n.toFixed(2).replace('.', ',').replace(/\d{3}(?=(\d{3})*,)/g, function (s) {
    return '.' + s
  })
}

console.log(calculations.map(format))