Gaussian/Banker's Rounding in Javascript

Question

I have been using Math.Round(myNumber, MidpointRounding.ToEven) in c# to do my server-side rounding, however, the user needs to know 'live' what the result of the server-side operation will be which means (avoiding an ajax request) creating a javascript method to replicate the MidpointRounding.ToEven method used by c#.

MidpointRounding.ToEven is Gaussian/Bankers rounding, a very common rounding method for accounting systems described here.

Does anyone have any experience with this? I have found examples online but they do not round to a given number of decimal places...

Answer 1

You could use Ajax to actually execute this rounding on the server side which will make it simpler to maintain your code base, because you will only have one single code. If you decide to change it, you'll only change it once. No need for (maybe even complex) javascript updates.

Answer 2

function evenRound(num, decimalPlaces) {
    var d = decimalPlaces || 0;
    var m = Math.pow(10, d);
    var n = d ? num * m : num;
    var i = Math.floor(n), f = n - i;
    var r = (f == 0.5) ? ((i % 2 == 0) ? i : i + 1) : Math.round(n);
    return d ? r / m : r;
}

alert(evenRound(1.5)); // 2
alert(evenRound(2.5)); // 2
alert(evenRound(1.535, 2)); // 1.54
alert(evenRound(1.525, 2)); // 1.52