Padding for Strings and Numbers

annotated.js

function(
  s, // String / Number to pad
  l, // target length
  c, // character used for padding
  u  // undefined
){
  c=new Array( // reusing c to carry padding
    (l=        // reusing l to to carry padding length
      (l||0)   // target length or 0
      -(''+s)  // minus s.toString()
      .length  // .length
      +1       // plus 1
    )>0        // if greater than 0
    &&l        //   return l
    ||0        // else don't pad
    ).join(    // join array
      c!=u     // if we supplied a character
        ?c     //   the character
        :' '   // else space
      );
  return {
    l:c+s,     // left padding pad().l
    r:s+c,     // right padding pad().r
    toString:function(){ // default
      return c+s         // .toString()
    }                    // behavior
  }
}

example.js

var pad = function(s,l,c,u){c=new Array((l=(l||0)-(''+s).length+1)>0&&l||0).join(c!=u?c:' ');return {l:c+s,r:s+c,toString:function(){return c+s}}}

console.log(
  pad(15, 5, 0).l       // left padding
+ pad('foo', 5)         // js does .toString()
+ pad('bar', 5, '-').r  // right padding with -
)

// 00015  foobar--

index.js

function(s,l,c,u){c=new Array((l=(l||0)-(''+s).length+1)>0&&l||0).join(c!=u?c:' ');return {l:c+s,r:s+c,toString:function(){return c+s}}}

LICENSE.txt

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 George Stagas https://github.com/stagas

 Everyone is permitted to copy and distribute verbatim or modified
 copies of this license document, and changing it is allowed as long
 as the name is changed.

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WHAT THE FUCK YOU WANT TO.

package.json

{ "name": "pad"
, "description": "Padding for Strings and Numbers"
, "keywords": 
  [ "pad"
  , "padding"
  ]
}