BigDecimal in JavaScript

Question

I'm very new to JavaScript (I come from a Java background) and I am trying to do some financial calculations with small amounts of money.

My original go at this was:

<script type="text/javascript">
    var normBase = ("[price]").replace("$", "");
    var salesBase = ("[saleprice]").replace("$", "");
    var base;
    if (salesBase != 0) {
        base = salesBase;
    } else {
        base = normBase;
    }
    var per5  = (base - (base * 0.05));
    var per7  = (base - (base * 0.07));
    var per10 = (base - (base * 0.10));
    var per15 = (base - (base * 0.15));
    document.write
        (
        '5% Off: $'  + (Math.ceil(per5  * 100) / 100).toFixed(2) + '<br/>' +
        '7% Off: $'  + (Math.ceil(per7  * 100) / 100).toFixed(2) + '<br/>' +
        '10% Off: $' + (Math.ceil(per10 * 100) / 100).toFixed(2) + '<br/>' +
        '15% Off: $' + (Math.ceil(per15 * 100) / 100).toFixed(2) + '<br/>'
    );
</script>

This worked well except it always rounded up (Math.ceil). Math.floor has the same issue, and Math.round is also no good for floats.

In Java, I would have avoided the use of floats completely from the get-go, however in JavaScript there does not seem to be a default inclusion of something comparable.

The problem is, all the libraries mentioned are either broken or for a different purpose. The jsfromhell.com/classes/bignumber library is very close to what I need, however I'm having bizarre issues with its rounding and precision... No matter what I set the Round Type to, it seems to decide on its own. So for example, 3.7107 with precision of 2 and round type of ROUND_HALF_UP somehow winds up as 3.72 when it should be 3.71.

I also tried @JasonSmith BigDecimal library (a machined port from Java's BigDecimal), but it seems to be for node.js which I don't have the option of running.

How can I accomplish this using vanilla JavaScript (and be reliable) or is there a modern (ones mentioned above are all years old now) library that I can use that is maintained and is not broken?

Answer 1

I like using accounting.js for number, money and currency formatting.

Homepage - https://openexchangerates.github.io/accounting.js/

Github - https://github.com/openexchangerates/accounting.js