Javascript formatting a rounded number to N decimals

Question

in JavaScript  the typical way to round a number to N decimal places is something like   function roundNumber num  dec      return Math round num   Math pow 10  dec     Math pow 10  dec        x000D   x000D  function roundNumber num  dec    x000D    return Math round num   Math pow 10  dec     Math pow 10  dec   x000D    x000D   x000D  console log roundNumber 0 1   0 2  2    x000D  console log roundNumber 2 1234  2    x000D   x000D   x000D    However this approach will round to a maximum of N decimal places while I want to always round to N decimal places  For example  2 0  would be rounded to  2     Any ideas

User · Accepted Answer

That s not a rounding ploblem  that is a display problem  A number doesn t contain information about significant digits  the value 2 is the same as 2 0000000000000  It s when you turn the rounded value into a string that you have make it display a certain number of digits   You could just add zeroes after the number  something like   var s   number toString    if  s indexOf         -1  s         while  s length  lt  s indexOf        4  s     0      Note that this assumes that the regional settings of the client uses period as decimal separator  the code needs some more work to function for other settings

User · Answer

Hopefully working code  didn t do much testing    function toFixed value  precision        var precision   precision    0          neg   value  lt  0          power   Math pow 10  precision           value   Math round value   power           integral   String  neg   Math ceil   Math floor  value   power            fraction   String  neg   -value   value    power           padding   new Array Math max precision - fraction length  0    1  join  0         return precision   integral          padding   fraction   integral

User · Answer

I think below function can help   function roundOff value round       return  parseInt value    10     round   1    - parseInt value    10    round     10   gt  4      parseFloat parseInt  value   parseFloat 1    10    round       10    round         10    round      parseFloat parseInt value    10    round        10    round        usage   roundOff 600 23458 2   will return 600 23

User · Answer

If you do not really care about rounding  just added a toFixed x  and then removing trailing 0es and the dot if necessary  It is not a fast solution   function format value  decimals        if  value            value   value toFixed decimals                     else           value    0             if  value indexOf       lt  0    value               var dotIdx   value indexOf           while  value length - dotIdx  lt   decimals    value     0        add 0 s      return value

User · Answer

I found a way  This is Christoph s code with a fix   function toFixed value  precision        var precision   precision    0          power   Math pow 10  precision           absValue   Math abs Math round value   power            result    value  lt  0    -          String Math floor absValue   power         if  precision  gt  0            var fraction   String absValue   power               padding   new Array Math max precision - fraction length  0    1  join  0            result          padding   fraction            return result      Read the details of repeating a character using an array constructor here if you are curious as to why I added the    1

User · Answer

There s always a better way for doing things   var number   51 93999999999761    I would like to get four digits precision  51 94  just do   number toPrecision 4     the result will be  51 94

User · Answer

PHP-Like rounding Method  The code below can be used to add your own version of Math round to your own namespace which takes a precision parameter  Unlike Decimal rounding in the example above  this performs no conversion to and from strings  and the precision parameter works same way as PHP and Excel whereby a positive 1 would round to 1 decimal place and -1 would round to the tens   var myNamespace       myNamespace round   function number  precision        var factor   Math pow 10  precision       var tempNumber   number   factor      var roundedTempNumber   Math round tempNumber       return roundedTempNumber   factor      myNamespace round 1234 5678  1      1234 6 myNamespace round 1234 5678  -1      1230   from Mozilla Developer reference for Math round

User · Answer

I think that there is a more simple approach to all given here  and is the method Number toFixed   already implemented in JavaScript   simply write   var myNumber   2   myNumber toFixed 2     returns  2 00  myNumber toFixed 1     returns  2 0    etc

User · Answer

This works for rounding to N digits  if you just want to truncate to N digits remove the Math round call and use the Math trunc one    function roundN value  digits       var tenToN   10    digits     return   Math trunc   Math round value   tenToN     tenToN      Had to resort to such logic at Java in the past when I was authoring data manipulation E-Slate components  That is since I had found out that adding 0 1 many times to 0 you d end up with some unexpectedly long decimal part  this is due to floating point arithmetics    A user comment at Format number to always show 2 decimal places calls this technique scaling    Some mention there are cases that don t round as expected and at http   www jacklmoore com notes rounding-in-javascript  this is suggested instead   function round value  decimals      return Number Math round value  e  decimals   e-  decimals

[javascript] Javascript: formatting a rounded number to N decimals

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