Round float values in JavaScript

Question

I am trying to round a value in JS but I am getting not rounded value, this is what I have:

  $(document).on("click", ".open-AddBookDialog", function () {
              var agentPercentage = parseFloat($('#<%=ddlSplitPerc.ClientID%>').val()).toFixed(2);
              var percMod = 1.0 - agentPercentage;
              percMod = Math.ceil(percMod * 100) / 100;
              var dropdownAgentPerc = $('#<%=ddlPercSplitAgent.ClientID %>');
              dropdownAgentPerc.val(percMod);
             dropdownAgentPerc.change();           
             $('#AddNewSplitAgentLife').modal('show');
          });

For example, the agentPercentage is 0.7 and when I am subtracting 1 - 0.7 I am getting this value:

0.30000000000000004

What do you think I should change? I tried the Math.cell example as well but I am getting 0.31 as a result.

So you're saying that you're surprised that floating point mathematics are not precise on a computer? — Tomalak, Aug 13 '13 at 19:52
This tells you why you're getting that result: [Is JavaScript's Floating-Point Math Broken?](http://stackoverflow.com/questions/588004/is-javascripts-floating-point-math-broken) — bfavaretto, Aug 13 '13 at 19:55

score 3 · Accepted Answer · edited May 23 '17 at 12:01

3

The solution is in another question already asked: Dealing with float precision in Javascript

(Math.floor(y/x) * x).toFixed(2);

edited May 23 '17 at 12:01

Community

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answered Aug 13 '13 at 19:52

jerone

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thx for your answer but how can I utilize that formula in my case? I am not doing any dividing, I tried (Math.floor(1 - 0.7) * 1) but I am getting 0 as a result. Thanks – Laziale Aug 13 '13 at 19:59
1

You only need the `.toFixed(2)` part. – jerone Aug 13 '13 at 20:02

score 0 · Answer 2 · answered Aug 13 '13 at 20:11

It should work if you subtract .5 from the value you pass to Math.ceil

percMod = Math.ceil((percMod * 100) -.5 )/ 100;

Math.ceil will round up for any decimal above .000

So to simulate the typical rounding behavior of only rounding decimals above .500 you should subtract .5

Round float values in JavaScript

2 Answers2