How to output numbers with leading zeros in JavaScript

Question

Is there a way to prepend leading zeros to numbers so that it results in a string of fixed length  For example  5 becomes  quot 05 quot  if I specify 2 places

User · Answer

Just for fun  I had some time to kill   a more sophisticated implementation which caches the zero-string   pad zeros   new Array 5  join  0    function pad num  len        var str   String num           diff   len - str length      if diff  lt   0  return str      if diff  gt  pad zeros length          pad zeros   new Array diff   1  join  0        return pad zeros substr 0  diff    str      If the padding count is large and the function is called often enough  it actually outperforms the other methods

User · Answer

function zfill num  len   return  Array len  join  0     num  slice -len

User · Answer

NOTE  Potentially outdated  ECMAScript 2017 includes String prototype padStart   You ll have to convert the number to a string since numbers don t make sense with leading zeros  Something like this  function pad num  size        num   num toString        while  num length  lt  size  num    quot 0 quot    num      return num     Or  if you know you d never be using more than X number of zeros  this might be better  This assumes you d never want more than 10 digits  function pad num  size        var s    quot 000000000 quot    num      return s substr s length-size      If you care about negative numbers you ll have to strip the - and read it

User · Answer

From https   gist github com 1180489 function pad a  b     return 1e15   a       slice -b      With comments  function pad    a     the number to convert    b    number of resulting characters      return       1e15   a      combine with large number      quot  quot     convert to string     slice -b     cut leading  quot 1 quot

User · Answer

You could extend the Number object   Number prototype pad   function size        var s   String this       while  s length  lt   size    2    s    0    s       return s      Examples    9  pad       returns  09    7  pad 3      returns  007

User · Answer

UPDATE  Small one-liner function using the ES2017 String prototype padStart method    x000D   x000D  const zeroPad    num  places    gt  String num  padStart places   0   x000D   x000D  console log zeroPad 5  2        05  x000D  console log zeroPad 5  4        0005  x000D  console log zeroPad 5  6        000005  x000D  console log zeroPad 1234  2        1234  x000D   x000D   x000D    Another ES5 approach   function zeroPad num  places      var zero   places - num toString   length   1    return Array   zero  gt  0  amp  amp  zero   join  0     num     zeroPad 5  2       05  zeroPad 5  4       0005  zeroPad 5  6       000005  zeroPad 1234  2       1234

[javascript] How to output numbers with leading zeros in JavaScript?

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