How to format a float in javascript

Question

In JavaScript  when converting from a float to a string  how can I get just 2 digits after the decimal point  For example  0 34 instead of 0 3445434

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function trimNumber num  len      const modulu one   1    const start numbers float 2    var int part   Math trunc num     var float part   String num   modulu one         float part   float part slice start numbers float  start numbers float len     return int part     float part

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x000D   x000D  countDecimals   value   gt        if  Math floor value      value  return 0      let stringValue   value toString   split      1       if  stringValue          return value toString   split      1  length           value toString   split      1  length           0        else         return 0                formatNumber  ans   gt       let decimalPlaces   this countDecimals ans       ans   1   ans      if  decimalPlaces     0          let onePlusAns   ans   1        let decimalOnePlus   this countDecimals onePlusAns         if  decimalOnePlus  lt  decimalPlaces            ans   ans toFixed decimalPlaces - 1  replace     0                  else           let tenMulAns   ans   10          let decimalTenMul   this countDecimals tenMulAns           if  decimalTenMul   1  lt  decimalPlaces              ans   ans toFixed decimalPlaces - 1  replace     0                                    x000D   x000D   x000D   I just add 1 to the value and count the decimal digits present in the original value and the added value  If I find the decimal digits after adding one less than the original decimal digits  I just call the toFixed   with  original decimals - 1   I also check by multiplying the original value by 10 and follow the same logic in case adding one doesn t reduce redundant decimal places  A simple workaround to handle floating-point number rounding in JS  Works in most cases I tried

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The key here I guess is to round up correctly first  then you can convert it to String   function roundOf n  p        const n1   n   Math pow 10  p   1       const n2   Math floor n1   10       if  n1  gt    n2   10   5             return  n2   1    Math pow 10  p             return n2   Math pow 10  p         All edge cases listed in this thread roundOf 95 345  2      95 35 roundOf 95 344  2      95 34 roundOf 5 0364342423  2      5 04 roundOf 0 595  2      0 60 roundOf 0 335  2      0 34 roundOf 0 345  2      0 35 roundOf 551 175  2      551 18 roundOf 0 3445434  2      0 34   Now you can safely format this value with toFixed p   So with your specific case   roundOf 0 3445434  2  toFixed 2      0 34

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One more problem to be aware of  is that toFixed   can produce unnecessary zeros at the end of the number  For example   var x  23-7 37  x 15 629999999999999 x toFixed 6   15 630000    The idea is to clean up the output using a RegExp   function humanize x     return x toFixed 6  replace     0             The RegExp matches the trailing zeros  and optionally the decimal point  to make sure it looks good for integers as well   humanize 23-7 37   15 63  humanize 1200   1200  humanize 1200 03   1200 03  humanize 3 4   0 75  humanize 4 3   1 333333

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don t spend 5 minutes  use my code     function prettyFloat x nbDec         if   nbDec  nbDec   100      var a   Math abs x       var e   Math floor a       var d   Math round  a-e  nbDec   if  d    nbDec    d 0  e          var signStr    x lt 0     -             var decStr   d toString    var tmp   10  while tmp lt nbDec  amp  amp  d tmp  lt  nbDec   decStr    0  decStr  tmp  10       var eStr   e toString        return signStr eStr     decStr     prettyFloat 0             0 00  prettyFloat -1           -1 00  prettyFloat -0 999       -1 00  prettyFloat 0 5           0 50

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Maybe you ll also want decimal separator  Here is a function I just made   function formatFloat num casasDec sepDecimal sepMilhar        if  num  lt  0                num   -num          sinal   -1        else         sinal   1      var resposta           var part           if  num    Math floor num      decimal values present               part   Math round  num-Math floor num   Math pow 10 casasDec   toString       transforms decimal part into integer  rounded          while  part length  lt  casasDec              part    0  part          if  casasDec  gt  0                        resposta   sepDecimal part              num   Math floor num             else             num   Math round num            end of decimal part     while  num  gt  0     integer part               part    num - Math floor num 1000  1000  toString       part   three less significant digits         num   Math floor num 1000           if  num  gt  0              while  part length  lt  3     123 023 123  if sepMilhar                       part    0  part     023         resposta   part resposta          if  num  gt  0              resposta   sepMilhar resposta            if  sinal  lt  0          resposta    -  resposta      return resposta

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There is no way to avoid inconsistent rounding for prices with x xx5 as actual value using either multiplication or division  If you need to calculate correct prices client-side you should keep all amounts in cents  This is due to the nature of the internal representation of numeric values in JavaScript  Notice that Excel suffers from the same problems so most people wouldn t notice the small errors caused by this phenomen  However errors may accumulate whenever you add up a lot of calculated values  there is a whole theory around this involving the order of calculations and other methods to minimize the error in the final result  To emphasize on the problems with decimal values  please note that 0 1   0 2 is not exactly equal to 0 3 in JavaScript  while 1   2 is equal to 3

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I use this code to format floats  It is based on toPrecision   but it strips unnecessary zeros  I would welcome suggestions for how to simplify the regex   function round x  n        var exp   Math pow 10  n       return Math floor x exp   0 5  exp      Usage example   function test x  n  d        var rounded   rnd x  d       var result   rounded toPrecision n       result   result replace     0              result   result replace     0 e    e        result   result replace  e     e        return result       document write test 1 2000e45  3  2           1 2e45      lt br gt     document write test 1 2000e 45  3  2           1 2e45      lt br gt     document write test 1 2340e45  3  2           1 23e45      lt br gt     document write test 1 2350e45  3  2           1 24e45      lt br gt     document write test 1 0000  3  2           1      lt br gt     document write test 1 0100  3  2           1 01      lt br gt     document write test 1 2340  4  2           1 23      lt br gt     document write test 1 2350  4  2           1 24      lt br gt

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Be careful when using toFixed     First  rounding the number is done using the binary representation of the number  which might lead to unexpected behaviour  For example   0 595  toFixed 2       0 59    instead of  0 6    Second  there s an IE bug with toFixed    In IE  at least up to version 7  didn t check IE8   the following holds true    0 9  toFixed 0       0    It might be a good idea to follow kkyy s suggestion or to use a custom toFixed   function  eg  function toFixed value  precision        var power   Math pow 10  precision    0       return String Math round value   power    power

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There are functions to round numbers  For example   var x   5 0364342423  print x toFixed 2      will print 5 04   EDIT  Fiddle

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If you want the string without round you can use this RegEx  maybe is not the most efficient way    but is really easy    2 34567778  toString   match   d    d 2    0      2 34

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var x   0 3445434 x   Math round  x 100    100    this will make nice rounding

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There is a problem with all those solutions floating around using multipliers  Both kkyy and Christoph s solutions are wrong unfortunately   Please test your code for number 551 175 with 2 decimal places - it will round to 551 17 while it should be 551 18   But if you test for ex  451 175 it will be ok - 451 18  So it s difficult to spot this error at a first glance   The problem is with multiplying  try 551 175   100   55117 49999999999  ups    So my idea is to treat it with toFixed   before using Math round     function roundFix number  precision        var multi   Math pow 10  precision       return Math round   number   multi  toFixed precision   1      multi

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var result   Math round original 100  100    The specifics  in case the code isn t self-explanatory   edit     or just use toFixed  as proposed by Tim B  the  Forgot that one  thanks  and an upvote  for reminder

[javascript] How to format a float in javascript?

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