How can I pad a value with leading zeros

Question

What is the recommended way to zerofill a value in JavaScript  I imagine I could build a custom function to pad zeros on to a typecasted value  but I m wondering if there is a more direct way to do this   Note  By  zerofilled  I mean it in the database sense of the word  where a 6-digit zerofilled representation of the number 5 would be  000005

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I am using this simple approach  var input   1000    input any number var len   input toString   length  for  i   1  i  lt  input  i        console log  MyNumber       000000000000000    i  slice -len

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I actually had to come up with something like this recently  I figured there had to be a way to do it without using loops   This is what I came up with   function zeroPad num  numZeros        var n   Math abs num       var zeros   Math max 0  numZeros - Math floor n  toString   length        var zeroString   Math pow 10 zeros  toString   substr 1       if  num  lt  0             zeroString    -    zeroString             return zeroString n      Then just use it providing a number to zero pad    gt  zeroPad 50 4    0050    If the number is larger than the padding  the number will expand beyond the padding    gt  zeroPad 51234  3    51234    Decimals are fine too    gt  zeroPad 51 1234  4    0051 1234    If you don t mind polluting the global namespace you can add it to Number directly   Number prototype leftZeroPad   function numZeros        var n   Math abs this       var zeros   Math max 0  numZeros - Math floor n  toString   length        var zeroString   Math pow 10 zeros  toString   substr 1       if  this  lt  0             zeroString    -    zeroString             return zeroString n      And if you d rather have decimals take up space in the padding   Number prototype leftZeroPad   function numZeros        var n   Math abs this       var zeros   Math max 0  numZeros - n toString   length        var zeroString   Math pow 10 zeros  toString   substr 1       if  this  lt  0             zeroString    -    zeroString             return zeroString n      Cheers       XDR came up with a logarithmic variation that seems to perform better   WARNING  This function fails if num equals zero  e g  zeropad 0  2    function zeroPad  num  numZeros        var an   Math abs  num       var digitCount   1   Math floor  Math log  an    Math LN10       if  digitCount  gt   numZeros            return num            var zeroString   Math pow  10  numZeros - digitCount  toString    substr  1       return num  lt  0    -    zeroString   an   zeroString   an        Speaking of performance  tomsmeding compared the top 3 answers  4 with the log variation    Guess which one majorly outperformed the other two

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The quick and dirty way   y    new Array count   1 - x toString   length   join  0     x    For x   5 and count   6 you ll have y    000005

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Here s a quick function I came up with to do the job  If anyone has a simpler approach  feel free to share   function zerofill number  length           Setup     var result   number toString        var pad   length - result length       while pad  gt  0            result    0    result          pad--             return result

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variable-length padding function  function addPaddingZeroes value  nLength        var sValue   value         converts to string      if sValue length gt  nLength          return sValue      else               for var nZero   0  nZero  lt  nLength  nZero                sValue    0    sValue          return  sValue  substring nLength - sValue length  nLength

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function pad toPad  padChar  length       return  String toPad  length  lt  length            new Array length - String toPad  length   1  join padChar    String toPad            toPad      pad 5  0  6         000005  pad  10   0  2      10     don t pad if not necessary  pad  S    O   2     SO     etc   Cheers

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A simple elegant solution  where n is the number and l is the length   function nFill  n  l   return  l gt n toString   length    Array l  join  0   n  slice -l   n    This keeps the length if it is over desired  as not to alter the number    x000D   x000D  n   500  x000D   x000D  console log nFill n  5    x000D  console log nFill n  2    x000D   x000D  function nFill  n  l   return  l gt n toString   length    Array l  join  0   n  slice -l   n   x000D   x000D   x000D

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ES6 makes this fairly trivial   function pad  num  length  countSign   true      num   num toString     let negative   num startsWith  -     let numLength   negative  amp  amp   countSign   num length - 1   num length   if  numLength  gt   length        return num     else if  negative        return  -     0  repeat length - numLength    num substr 1      else       return  0  repeat length - numLength    num        pad 42  4                0042  pad 12345  4             12345  pad -123  4              -100  pad -123  4  false       -0100

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Ok  ok  I can t believe I m bothering to submit another answer to this one  but I think my approach is a little different  The reason I needed to pad a number was to display it in a  lt pre gt  element  part of an on-screen log   so it s ultimately going to be a string anyway  Instead of doing any math  I wrote a simple function to overlay a string value on a mask string   function overlayr m  s      return m length  gt  s length   m substr 0  m length - s length    s   s      The benefit of this is that I can use it for all sorts of string alignment tasks  To call it  just pass in the mask and number as a string    gt  overlayr  00000    5  toString     lt   00005    As an added bonus  it deals with overflows correctly    gt  overlayr  00000    555555  toString     lt   555555    And of course it s not limited to 0 padding    gt  overlayr           55  toString     lt      55

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Just an another solution  but I think it s more legible    x000D   x000D  function zeroFill text  size  x000D    x000D    while  text length  lt  size   x000D     text    0    text  x000D      x000D     x000D    return text  x000D    x000D   x000D   x000D

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Unfortunately  there are a lot of needless complicated suggestions for this problem  typically involving writing your own function to do math or string manipulation or calling a third-party utility   However  there is a standard way of doing this in the base JavaScript library with just one line of code   It might be worth wrapping this one line of code in a function to avoid having to specify parameters that you never want to change like the local name or style   var amount   5   var text   amount toLocaleString  en-US         style   decimal       minimumIntegerDigits  3      useGrouping  false       This will produce the value of  005  for text   You can also use the toLocaleString function of Number to pad zeros to the right side of the decimal point   var amount   5   var text   amount toLocaleString  en-US         style   decimal       minimumFractionDigits  2      useGrouping  false       This will produce the value of  5 00  for text   Change useGrouping to true to use comma separators for thousands   Note that using toLocaleString   with locales and options arguments is standardized separately in ECMA-402  not in ECMAScript  As of today  some browsers only implement basic support  i e  toLocaleString   may ignore any arguments   Complete Example

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Some monkeypatching also works  String prototype padLeft   function  n  c      if  isNaN n       return null    c   c     0     return  new Array n  join c  substring 0  this length-n     this      var paddedValue    123  padLeft 6      returns  000123  var otherPadded    TEXT  padLeft 8           returns      TEXT

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I can t believe all the complex answers on here    Just use this   var zerofilled     0000  n  slice -4

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Why not use recursion   function padZero s  n        s   s toString       in case someone passes a number     return s length  gt   n   s   padZero  0    s  n

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just wanted to make the comment  but i don t have enough points  that the highest voted answer fails with negative numbers and decimals  function padNumber n pad        p   Math pow 10 pad       a   Math abs n       g    n lt 0       return  a  lt  p       g    -           p a  toString   substring 1     n     padNumber  -31 235  5     -00031 235

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The following provides a quick and fast solution    x000D   x000D  function numberPadLeft num   max  padder    0    x000D       return        num               x000D         dif   max - num length  dif  gt  0   x000D       padder repeat dif  lt  0   0   dif    num   x000D       num   x000D    x000D   x000D   x000D

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Just an FYI  clearer  more readable syntax IMHO   use strict   String prototype pad   function  len  c  left         var s               c     c                   len   Math max  len  0   - this length          left     left    false        while  s length  lt  len     s    c        return   left     s   this       this   s        Number prototype pad   function  len  c  left         return String  this   pad  len  c  left      Number prototype lZpad   function  len         return this pad  len   0   true        This also results in less visual and readability glitches of the results than some of the other solutions  which enforce  0  as a character  answering my questions what do I do if I want to pad other characters  or on the other direction  right padding   whilst remaining easy to type  and clear to read  Pretty sure it s also the DRY est example  with the least code for the actual leading-zero-padding function body  as the other dependent functions are largely irrelevant to the question    The code is available for comment via gist from this github user  original source of the code  https   gist github com Lewiscowles1986 86ed44f428a376eaa67f  A note on console  amp  script testing  numeric literals seem to need parenthesis  or a variable in order to call methods  so 2 pad      will cause an error  whilst  2  pad 0      will not  This is the same for all numbers it seems

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function numberPadding n  p      n   n toString      var len   p - n length    if  len  gt  0        for  var i 0  i  lt  len  i            n    0    n              return n

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This one is less native  but may be the fastest     zeroPad   function  num  count        var pad    num       length - count      while --pad  gt  -1            num    0    num            return num

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function zeroFill number  width        width -   number toString   length -      test number        if  width  gt  0            return new Array width   1  join  0     number            return number          always return a string     Slight changes made to Peter s code  With his code if the input is  1 2  3  the value returned should be 01 2 but it is returning 1 2   The changes here should correct that

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My little contribution with this topic  https   gist github com lucasferreira a881606894dde5568029       Autor  Lucas Ferreira - http   blog lucasferreira com   Usage  fz 9  or fz 100  7     function fz o  s        for var s Math max   s  2   n    Math abs o   length   n length lt s   n  0  n        return   o  lt  0    -          n       Usage   fz 9   amp  fz 9  2      09  fz -3  2      -03  fz 101  7      0000101    I know  it s a pretty dirty function  but it s fast and works even with negative numbers

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was here looking for a standard  had the same idea as Paul and Jonathan    theirs are super cute  here s a horrible-cute version   function zeroPad n l i       return  i n Math pow 10 l   i gt 1    n i toFixed l  replace  0            works too  we re assuming integers  yes        gt  zeroPad Math pow 2  53   20    00009007199254740992   gt  zeroPad -Math pow 2  53   20    -00009007199254740992   gt  zeroPad Math pow 2  53   10    9007199254740992   gt  zeroPad -Math pow 2  53   10    -9007199254740992

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I use this snipet to get a 5 digits representation   value 100000  toString   slice -5      00123  with value 123

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My solution  Number prototype PadLeft   function  length  digit        var str        this      while  str length  lt  length            str    digit     0     str            return str       Usage  var a   567 25  a PadLeft 10      0000567 25  var b   567 25  b PadLeft 20   2       22222222222222567 25

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sprintf js is a complete open source JavaScript sprintf implementation   for the browser and node js       Its prototype is simple   string sprintf string format    mixed arg1    mixed arg2               I d like to recommend sprintf module from Alexandru Mara teanu throughout the solution would simply looks like   var sprintf   require  sprintf    var zeroFilled   sprintf   06d   5    console log zeroFilled      000005      Note  I m answering this question 6 years later but it seems that this   question becomes a  javascript zero leading  reference considering   it s high number of views and answers

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function uint zerofill num  width        var pad       num            for  var i   num length  i  lt  width  i            pad     0       return pad   num

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Not that this question needs more answers  but I thought I would add the simple lodash version of this     padLeft number  6   0

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The power of Math   x   integer to pad y   number of zeroes to pad  function zeroPad x  y       y   Math max y-1 0      var n    x   Math pow 10 y   toFixed y      return n replace

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A simple short recursive function to achieve your proposal    function padleft  YourNumber  OutputLength       if  YourNumber length  gt   OutputLength            return YourNumber        else           return padleft  0   YourNumber  OutputLength              YourNumber is the input number  OutputLength is the preferred output number length  with 0 padding left     This function will add 0 on the left if your input number length is shorter than the wanted output number length

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In all modern browsers you can use  numberStr padStart numberLength   0       x000D   x000D  function zeroFill num  numLength    x000D    var numberStr   num toString    x000D   x000D    return numberStr padStart numLength   0    x000D    x000D   x000D  var numbers    0  1  12  123  1234  12345   x000D   x000D  numbers forEach  x000D    function num    x000D      var numString   num toString    x000D       x000D      var paddedNum   zeroFill numString  5   x000D   x000D      console log paddedNum   x000D      x000D     x000D   x000D   x000D    Here is the MDN reference https   developer mozilla org en-US docs Web JavaScript Reference Global Objects String padStart

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Modern browsers now support padStart  you can simply now do  string padStart maxLength   quot 0 quot     Example   x000D   x000D  string    14   maxLength   5     maxLength is the max string length  not max   of fills res   string padStart maxLength   0    console log res      prints  00014   number   14  maxLength   5     maxLength is the max string length  not max   of fills res   number toString   padStart maxLength   0    console log res      prints  00014  x000D   x000D   x000D

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Yet another version    function zPad s n       return  new Array n 1  join  0   s  substr -Math max n s toString   length

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I came up with an absurd one-liner while writing a numeric base converter   Didn t see anything quite like it in the other answers  so here goes   x000D   x000D     This is cursed function p i w z  z z  0 w w  8 i     var o i length w return o     Array w-o  fill z     i  join     i    console log p 8675309              Default  pad w  0 to 8 digits console log p 525600  10           Pad to 10 digits console log p 69420  10   X        Pad w  X to 10 digits console log p 8675309  4           Pad to next 4 digits console log p 12345678             Don t pad if you ain t gotta pad x000D   x000D   x000D   Or  in a form that doesn t quite as readily betray that I ve sold my soul to the Black Perl  function pad input  width  zero        zero   zero    0  width   width    8      Defaults     input                                     Convert input to string first          var overflow   input length   width       Do we overflow      if  overflow                              Yep   Let s pad it            var needed   width - overflow            to the next boundary            var zeroes   Array needed                with an array            zeroes   zeroes fill zero                full of our zero character            var output       zeroes    input         and concat those zeroes to input            output   output join                     and finally stringify        else           var output   input                    We don t overflow  no action needed                   return output                             Done     One thing that sets this apart from the other answers is that it takes a modulo of the number s length to the target width rather than a simple greater-than check   This is handy if you want to make sure the resulting length is some multiple of a target width  e g  you need the output to be either 5 or 10 characters long   No idea how well it performs  but hey  at least it s already minified

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I just stumbled upon this post looking for a native solution  Since there isn t a built-in solution  here s my take on it   function zerofill number  width        var num           while  width--  gt  0            num     0              return num slice 0  -  number       length    number

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With ES6  JavaScript  You can  quot zerofill a number quot  with something like the following function          param number The number     param minLength Minimal length for your string with leading zeroes     return Your formatted string     function zerofill nb  minLength           Convert your number to string      let nb2Str   nb toString           Guess the number of zeroes you will have to write      let nbZeroes   Math max 0  minLength - nb2Str length          Compute your result      return      0  repeat nbZeroes      nb2Str       console log zerofill 5  6         Displays  quot 000005 quot   With ES2017           param number The number     param minLength Minimal length for your string with leading zeroes     return Your formatted string     const zerofill    nb  minLength    gt  nb toString   padStart minLength   0    console log zerofill 5  6         Displays  quot 000005 quot

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This is an angular provider that I wrote  which makes use of  profitehlolz  s answer but employs memoization so that commonly used pad length-pad character combinations will not invoke the array build join needlessly   angular module  stringUtilities            service  stringFunctions    function             this padMemo              this padLeft function inputString padSize padCharacter                 var memoKey padSize    padCharacter               if  this padMemo memoKey                      this padMemo memoKey   new Array 1   padSize  join padCharacter                             var pad this padMemo memoKey              return  pad   inputString  slice -pad length

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function zeroPad num digits   return   num Math pow 10 digits       slice 2

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I have 2 solutions  The first is the real basic one to bad a number with zeros if you know that s all you want to do quickly   The second will also pad negative numbers - same as the  clever  solution that seems to have the best answer score   Here goes    x000D   x000D     One liner simple mode  x000D      always ensure the number is 6 digits long knowing its never negative  x000D  var mynum   12  x000D  var mynum2    0  repeat  n 6-mynum toString   length  gt 0 n 0  mynum  x000D  alert  One liner to pad number to be 6 digits long   Was   mynum   Now   mynum2   x000D   x000D     As a function which will also pad negative numbers x000D     Yes  i could do a check to only take  -  into account x000D     if it was passed in as an integer and not a string but x000D     for this  i haven t  x000D      x000D      s The string or integer to pad x000D      l The minumum length of  s x000D      c The character to pad with x000D      return updated string x000D  function padme s l c   x000D      s   s toString    x000D      c   c toString    x000D      m   s substr 0 1    -   x000D      return  m  -      c repeat  n l- s length- m 1 0    gt 0 n 0  s substr  m 1 0    x000D    x000D  alert  pad -12 to ensure it is 8 digits long     padme -12 8 0    x000D  alert  pad  hello  with  x  to ensure it is 12 digits long     padme  hello  12  x     x000D   x000D   x000D

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I didn t see anyone point out the fact that when you use String prototype substr   with a negative number it counts from the right   A one liner solution to the OP s question  a 6-digit zerofilled representation of the number 5  is    x000D   x000D  console log   00000000    5  substr -6    x000D   x000D   x000D    Generalizing we ll get    x000D   x000D  function pad num  len    return   00000000    num  substr -len     x000D   x000D  console log pad 5  6    x000D  console log pad 45  6    x000D  console log pad 345  6    x000D  console log pad 2345  6    x000D  console log pad 12345  6    x000D   x000D   x000D

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If you use Lodash    x000D   x000D  var n   1  x000D   x000D  alert    padLeft n  2  0        01 x000D   x000D  n   10  x000D   x000D  alert    padLeft n  2  0        10 x000D   lt script src  https   cdnjs cloudflare com ajax libs lodash js 3 10 0 lodash min js  gt  lt  script gt  x000D   x000D   x000D

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The latest way to do this is much simpler   var number   2 number toLocaleString undefined   minimumIntegerDigits 2     output   02

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This is the ES6 solution    x000D   x000D  function pad num  len    x000D    return  0  repeat len - num toString   length    num  x000D    x000D  alert pad 1234 6    x000D   x000D   x000D

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Here s what I used to pad a number up to 7 characters     0000000    number  slice -7    This approach will probably suffice for most people   Edit  If you want to make it more generic you can do this     0  repeat padding    number  slice -padding    Edit 2  Note that since ES2017 you can use String prototype padStart   number toString   padStart padding   0

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Our tests were bogus because mine had a typo   zeroPad   function  num  count        return   num   Math pow 10  count         substr 2        Paul s is the fastest  but I think  substr is faster than  slice even if it is one character more

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A little math can give you a one-line function   function zeroFill  number  width       return Array width - parseInt Math log number  Math LN10    join  0     number      That s assuming that number is an integer no wider than width  If the calling routine can t make that guarantee  the function will need to make some checks   function zeroFill  number  width         var n   width - parseInt Math log number  Math LN10       return  n  lt  0         number   Array n  join  0     number

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I really don t know why  but no one did it in the most obvious way  Here it s my implementation   Function       Pad a number with 0 on the left    function zeroPad number  digits        var num   number         while num length  lt  digits           num  0  num            return num      Prototype   Number prototype zeroPad function digits       var num this         while num length  lt  digits           num  0  num            return num        Very straightforward  I can t see any way how this can be any simpler  For some reason I ve seem many times here on SO  people just try to avoid  for  and  while  loops at any cost  Using regex will probably cost way more cycles for such a trivial 8 digit padding

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Don t reinvent the wheel  use underscore string   jsFiddle  var numToPad    5    alert   str pad numToPad  6   0        yields   000005

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Note to readers       As commenters have pointed out  this solution is  clever   and as   clever solutions often are  it s memory intensive and relatively   slow  If performance is a concern for you  don t use this solution       Potentially outdated  ECMAScript 2017 includes String prototype padStart and Number prototype toLocaleString is there since ECMAScript 3 1  Example   var n -0 1  n toLocaleString  en    minimumIntegerDigits 4 minimumFractionDigits 2 useGrouping false            will output  -0000 10       or  const padded     1     padStart 6  0     -  padded            will output  -0000 1     A simple function is all you need  function zeroFill  number  width       width -  number toString   length    if   width  gt  0           return new Array  width         test  number     2   1    join   0      number        return number          always return a string     you could bake this into a library if you want to conserve namespace or whatever   Like with jQuery s extend

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If npm is available in your environment some of ready-made packages can be used  www npmjs com browse keyword zeropad   I like zero-fill   Installation    npm install zero-fill   Usage  var zeroFill   require  zero-fill    zeroFill 4  1           0001   zeroFill 4  1              1  custom padding zeroFill 4  1           0001  partials

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My contribution   I m assuming you want the total string length to include the  dot   If not it s still simple to rewrite to add an extra zero if the number is a float   padZeros   function  num  zeros            return    num  lt  0     -          Array   zeros - String Math abs num   length  join  0     Math abs num

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I used   Utilities formatString   04d   iThe TWO to FOUR DIGIT     which gives up to 4 leading 0s  NOTE   THIS REQUIRES Google s apps-script Utilities     https   developers google com apps-script reference utilities utilities formatstringtemplate-args

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A simple function to do it   function padStr number  numDigits     return       number  lt  0    -               new Array numDigits   1  join  0          Math abs number   slice -numDigits

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If performance is really critical  looping over millions of records   an array of padding strings can be pre-generated  avoiding to do it for each call   Time complexity  O 1   Space complexity  O 1     x000D   x000D  const zeroPads   Array from   length  10        v    gt   0  repeat v   x000D   x000D  function zeroPad num  len    x000D    const numStr   String num  x000D    return  zeroPads len - numStr length    numStr  x000D    x000D   x000D   x000D

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Even later to the party   function zfill num  len      return 0  gt  num    -           Math pow 10  len   lt   Math abs num     0    Math abs num    Math pow 10  len    Math abs num   toString   substr 1      This handles negatives and situations where the number is longer than the field width  And floating-point

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function numPadding  padding i        return padding substr 0  padding length -  Math floor i  toString   length     Math floor i       numPadding  000000000  234   - gt   000000234    or  function numPadding  number  paddingChar i        var padding   new Array number   1  join paddingChar       return padding substr 0  padding length -  Math floor i  toString   length     Math floor i       numPadding 8   0   234   - gt   00000234

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Mnah     I have not seen a  ultimate  answer to this issue and if you are facing the same challenge I must save you some time by saying that saddly there s not built-in function for that on JavaScript  but there s this awesome function in PHP that does a great job on padding strings as well as numbers with single character or arbitrary strings so after some time of banging my head for not having the right tool on JS  mostly for zerofillin  numbers and usually for trimming strings to fit a fixed length  and excessive coding work I decided to write my own function that does the same   almost the same   read on for detail  that the dream PHP function but in comfortable client-side JavaScript   function str pad input pad length pad string pad type       var input input toString        var output         if  input length gt pad length  amp  amp  pad type   STR PAD RIGHT    var output input slice 0 pad length        else if  input length gt pad length  amp  amp  pad type   STR PAD LEFT    var output input slice input length-pad length input length        else if  input length lt pad length  amp  amp  pad type   STR PAD RIGHT             var caracteresNecesarios pad length-input length          var rellenoEnteros Math floor caracteresNecesarios pad string length           var rellenoParte caracteresNecesarios pad string length          var output input          for var i 0 i lt rellenoEnteros i    var output output pad string            var output output pad string slice 0 rellenoParte             else if  input length lt pad length  amp  amp  pad type   STR PAD LEFT             var caracteresNecesarios pad length-input length          var rellenoEnteros Math floor caracteresNecesarios pad string length           var rellenoParte caracteresNecesarios pad string length          var output             for var i 0 i lt rellenoEnteros i    var output output pad string            var output output pad string slice 0 rellenoParte           var output output input            else if input length  pad length  var output input        return output       The only thing that my function does not do is the STR PAD BOTH behavior that I could add with some time and a more comfortable keyboard  You might call the function and test it  bet you ll love it if you don t mind that inner code uses one or two words in Spanish    not big deal I think  I did not added comments for  watermarking  my coding so you can seamless use it in your work nor I compressed the code for enhanced readability  Use it and test it like this and spread the code   alert  str pad  murcielago  20  123   STR PAD RIGHT     str pad  murcielago  20  123   STR PAD RIGHT

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I didn t see any answer in this form so here my shot with regex and string manipulation    Works also for negative and decimal numbers   Code   function fillZeroes n   0  m   1      const p   Math max 1  m     return String n  replace   d    x   gt   0  repeat Math max p - x length  0     x       Some outputs   console log fillZeroes 6  2                gt  gt   06  console log fillZeroes 1 35  2             gt  gt   01 35  console log fillZeroes -16  3              gt  gt   -016  console log fillZeroes -1 456  3           gt  gt   -001 456  console log fillZeroes -456 53453  6       gt  gt   -000456 53453  console log fillZeroes  Agent 7   3        gt  gt   Agent 007

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To pad at the end of the number  use num toFixed  for example     document getElementById  el   value   amt toFixed 2     It s the simplest solution i ve found  and it works

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After a  long  long time of testing 15 different functions methods found in this questions answers  I now know which is the best  the most versatile and quickest    I took 15 functions methods from the answers to this question and made a script to measure the time taken to execute 100 pads  Each pad would pad the number 9 with 2000 zeros  This may seem excessive  and it is  but it gives you a good idea about the scaling of the functions   The code I used can be found here  https   gist github com NextToNothing 6325915  Feel free to modify and test the code yourself   In order to get the most versatile method  you have to use a loop  This is because with very large numbers others are likely to fail  whereas  this will succeed   So  which loop to use  Well  that would be a while loop  A for loop is still fast  but a while loop is just slightly quicker a couple of ms  - and cleaner   Answers like those by Wilco  Aleksandar Toplek or Vitim us will do the job perfectly   Personally  I tried a different approach  I tried to use a recursive function to pad the string number  It worked out better than methods joining an array but  still  didn t work as quick as a for loop   My function is   function pad str  max  padder      padder   typeof padder      undefined     0    padder    return str toString   length  lt  max   pad padder toString     str  max  padder    str      You can use my function with  or without  setting the padding variable  So like this   pad 1  3      Returns  001     - Or - pad 1  3   x       Returns  xx1    Personally  after my tests  I would use a method with a while loop  like Aleksandar Toplek or Vitim us  However  I would modify it slightly so that you are able to set the padding string   So  I would use this code   function padLeft str  len  pad        pad   typeof pad      undefined     0    pad           str   str           while str length  lt  len            str   pad   str            return str        Usage padLeft 1  3      Returns  001     - Or - padLeft 1  3   x       Returns  xx1    You could also use it as a prototype function  by using this code   Number prototype padLeft   function len  pad        pad   typeof pad      undefined     0    pad           var str   this           while str length  lt  len            str   pad   str            return str        Usage var num   1   num padLeft 3      Returns  001     - Or - num padLeft 3   x       Returns  xx1

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The simplest  most straight-forward solution you will find   function zerofill number length        var output   number toString        while output length  lt  length          output    0    output            return output

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Simple way  You could add string multiplication for the pad and turn it into a function   var pad    000000   var n    5   var result    pad n  slice -pad length     As a function   function paddy num  padlen  padchar        var pad char   typeof padchar      undefined    padchar    0       var pad   new Array 1   padlen  join pad char       return  pad   num  slice -pad length     var fu   paddy 14  5      00014 var bar   paddy 2  4              2

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Just for fun  here s my version of a pad function   function pad num  len      return Array len   1 - num toString   length  join  0     num      It also won t truncate numbers longer than the padding length

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function zFill n l       return         l  gt  n toString   length                Array l  join  0     n  slice -l      n

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First parameter is any real number  second parameter is a positive integer specifying the minimum number of digits to the left of the decimal point and third parameter is an optional positive integer specifying the number if digits to the right of the decimal point   function zPad n  l  r       return a String n  match    -    d       d      a 1   Array l  join 0  a 2   slice -Math max l a 2  length     undefined    typeof r  0 lt r          a 3  Array r 1  join 0   slice 0 r  a 3      a 3      0     so             zPad 6  2       06            zPad -6  2       -06         zPad 600 2  2       600 2          zPad -600  2       -600           zPad 6 2  3       006 2          zPad -6 2  3       -006 2        zPad 6 2  3  0       006          zPad 6  2  3       06 000      zPad 600 2  2  3       600 200  zPad -600 1499  2  3       -600 149

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A simple one for my use case  to fill milliseconds never   999  You can adjust the number of zeros for yours or use a more generic way if required           val integer     zeros padding     function zeroFill val  zeros        var str   val toString        if  str length  gt   zeros          return str      str    000    str      return str substring str length - zeros

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i wrote somethin in ecmaScript6  TypeScript  and perhaps someone can use it   class Helper                  adds leading 0 and returns string if value is not minSize long          else returns value as string                param  string number  value         param  number  minSize         returns  string              public static leadingNullString value  string number  minSize  number   string           if  typeof value     number                 value        value                    let outString  string               let counter  number   minSize - value length          if  counter  gt  0                for  let i   0  i  lt  counter  i                      outString     0                                   return  outString   value             Helper leadingNullString 123  2   returns  123   Helper leadingNullString 5  2   returns  05   Helper leadingNullString 40 2   returns  40   The ecmaScript4  JavaScript  transpilation looks like that   var Helper    function          function Helper               Helper leadingNullString   function  value  minSize            if  typeof value     number                 value        value                    var outString               var counter   minSize - value length          if  counter  gt  0                for  var i   0  i  lt  counter  i                      outString     0                                   return  outString   value              return Helper

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Maybe I am to naive  but I think that this works in one simple and efficient line of code  for positive numbers    padded    value Math pow 10 total length      slice 1    As long as you keep your length OK according to you set of values  as in any zero padding   this should work   The steps are    Add the power of 10 with the correct number of 0 s  69 1000   1069  Convert to string with      1069     1069   Slice the first 1  which resulted of first multiplication   1069      069     For natural listings  files  dirs     is quite useful

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exports pad    num  length    gt   0  repeat length - num toString   length    num

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Here s a little trick I think is cool   2 10000  toString   split  quot   quot   1   quot 0002 quot   52 10000  toString   split  quot   quot   1   quot 0052 quot

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ECMAScript 2017  use padStart or padEnd   abc  padStart 10                      abc   abc  padStart 10   foo         foofoofabc   abc  padStart 6  123465        123abc    More info    https   github com tc39 proposal-string-pad-start-end  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects String padStart

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If the fill number is known in advance not to exceed a certain value  there s another way to do this with no loops   var fillZeroes    00000000000000000000       max number of zero fill ever asked for in global  function zeroFill number  width           make sure it s a string     var input   number             var prefix           if  input charAt 0       -             prefix    -           input   input slice 1           --width            var fillAmt   Math max width - input length  0       return prefix   fillZeroes slice 0  fillAmt    input      Test cases here  http   jsfiddle net jfriend00 N87mZ

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Here a little array solution within a two line function  It checks also if the leading zeros are less than the length of the number string   function pad num  z        if  z  lt   num   num       length  return num      return Array   z - num length  join  0     num

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Late to the party here  but I often use this construct for doing ad-hoc padding of some value n  known to be a positive  decimal    offset   n       substr 1     Where offset is 10  digits   E g  Padding to 5 digits  where n   123    1e5   123       substr 1        gt  00123   The hexidecimal version of this is slightly more verbose    0x100000   0x123  toString 16  substr 1        gt  00123   Note 1  I like  profitehlolz s solution as well  which is the string version of this  using slice   s nifty negative-index feature

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This method isn t faster  but it s fairly native   zeroPad   function  num  count        return  Math pow 10  count - num toString   length   num  join     substr 1

[javascript] How can I pad a value with leading zeros?

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