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
– Tomalak, Commented Aug 13, 2013 at 19:52
This tells you why you're getting that result: Is JavaScript's Floating-Point Math Broken? — bfavaretto
– bfavaretto, Commented Aug 13, 2013 at 19:55

Community · Accepted Answer · 2017-05-23 12:01:37Z

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, 2017 at 12:01

CommunityBot

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answered Aug 13, 2013 at 19:52

jerone

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2 Comments

Laziale Over a year ago

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

jerone Over a year ago

You only need the .toFixed(2) part.

ken8367 · Accepted Answer · 2013-08-13 20:11:12Z

0

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

answered Aug 13, 2013 at 20:11

ken8367

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