JavaScript math round to two decimal places

Question

I have the following JavaScript syntax   var discount   Math round 100 -  price   listprice    100     This rounds up to the whole number  How can I return the result with two decimal places

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If you use a unary plus to convert a string to a number as documented on MDN   For example  discount toFixed 2

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The best and simple solution I found is  function round value  decimals     return Number Math round value  e  decimals   e-  decimals        round 1 005  2      1 01

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To get the result with two decimals  you can do like this    var discount   Math round  100 -  price   listprice    100    100    100    The value to be rounded is multiplied by 100 to keep the first two digits  then we divide by 100 to get the actual result

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I think the best way I ve seen it done is multiplying by 10 to the power of the number of digits  then doing a Math round  then finally dividing by 10 to the power of digits  Here is a simple function I use in typescript   function roundToXDigits value  number  digits  number        value   value   Math pow 10  digits       value   Math round value       value   value   Math pow 10  digits       return value      Or plain javascript   function roundToXDigits value  digits        if  digits           digits   2            value   value   Math pow 10  digits       value   Math round value       value   value   Math pow 10  digits       return value

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NOTE - See Edit 4 if 3 digit precision is important var discount    price   listprice  toFixed 2    toFixed will round up or down for you depending on the values beyond 2 decimals  Example  http   jsfiddle net calder12 tv9HY  Documentation  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Number toFixed Edit - As mentioned by others this converts the result to a string  To avoid this  var discount      price   listprice  toFixed 2     Edit 2- As also mentioned in the comments this function fails in some precision  in the case of 1 005 for example it will return 1 00 instead of 1 01  If accuracy to this degree is important I ve found this answer  https   stackoverflow com a 32605063 1726511 Which seems to work well with all the tests I ve tried  There is one minor modification required though  the function in the answer linked above returns whole numbers when it rounds to one  so for example 99 004 will return 99 instead of 99 00 which isn t ideal for displaying prices  Edit 3 - Seems having the toFixed on the actual return was STILL screwing up some numbers  this final edit appears to work  Geez so many reworks  var discount   roundTo  price   listprice   2    function roundTo n  digits      if  digits     undefined        digits   0         var multiplicator   Math pow 10  digits     n   parseFloat  n   multiplicator  toFixed 11      var test   Math round n    multiplicator     return   test toFixed digits       See Fiddle example here  https   jsfiddle net calder12 3Lbhfy5s  Edit 4 - You guys are killing me  Edit 3 fails on negative numbers  without digging into why it s just easier to deal with turning a negative number positive before doing the rounding  then turning it back before returning the result  function roundTo n  digits        var negative   false      if  digits     undefined            digits   0            if  n  lt  0            negative   true          n   n   -1            var multiplicator   Math pow 10  digits       n   parseFloat  n   multiplicator  toFixed 11        n    Math round n    multiplicator  toFixed digits       if  negative            n    n   -1  toFixed digits             return n     Fiddle  https   jsfiddle net 3Lbhfy5s 79

User · Answer

The functions Math round   and  toFixed   is meant to round to the nearest integer  You ll get incorrect results when dealing with decimals and using the  multiply and divide  method for Math round   or parameter for  toFixed    For example  if you try to round 1 005 using Math round 1 005   100    100 then you ll get the result of 1  and 1 00 using  toFixed 2  instead of getting the correct answer of 1 01   You can use following to solve this issue   Number Math round 100 -  price   listprice    100    e2      e-2      Add  toFixed 2  to get the two decimal places you wanted   Number Math round 100 -  price   listprice    100    e2      e-2   toFixed 2     You could make a function that will handle the rounding for you   function round value  decimals        return Number Math round value    e    decimals     e-    decimals       Example  https   jsfiddle net k5tpq3pd 36   Alternativ  You can add a round function to Number using prototype  I would not suggest adding  toFixed   here as it would return a string instead of number   Number prototype round   function decimals        return Number  Math round this    e    decimals      e-    decimals        and use it like this   var numberToRound   100 -  price   listprice    100  numberToRound round 2   numberToRound round 2  toFixed 2     Converts it to string with two decimals   Example https   jsfiddle net k5tpq3pd 35   Source  http   www jacklmoore com notes rounding-in-javascript

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A small variation on the accepted answer  toFixed 2  returns a string  and you will always get two decimal places  These might be zeros  If you would like to suppress final zero s   simply do this   var discount       price   listprice  toFixed 2      Edited  I ve just discovered what seems to be a bug in Firefox 35 0 1  which means that the above may give NaN with some values  I ve changed my code to   var discount   Math round price   listprice   100    100    This gives a number with up to two decimal places  If you wanted three  you would multiply and divide by 1000  and so on  The OP wants two decimal places always  but if toFixed   is broken in Firefox it needs fixing first  See https   bugzilla mozilla org show bug cgi id 1134388

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Fastest Way - faster than toFixed      TWO DECIMALS  x         123456 result   Math round x   100    100     result  12     THREE DECIMALS  x         123456 result   Math round x   1000    1000         result  123

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Here is a working example  var value 200 2365455  result Math round value 100  100      result will be 200 24

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To handle rounding to any number of decimal places  a function with 2 lines of code will suffice for most needs   Here s some sample code to play with         var testNum   134 9567654      var decPl   2      var testRes   roundDec testNum decPl         alert  testNum     rounded to     decPl     decimal places is     testRes        function roundDec nbr dec places           var mult   Math pow 10 dec places           return Math round nbr   mult    mult

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function round num dec              num   Math round num  e  dec        return Number num  e-  dec                Round to a decimal of your choosing      round 1 3453 2

User · Answer

try using discount toFixed 2

[javascript] JavaScript math, round to two decimal places

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