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annotated.js

function(
  a,  // input
  b,  // items in each group
  c,  // fillWith
  d,  // placeholder - index
  e   // placeholder - result
){
  d = -b,                           // set index
  e = [];                           // init result with an empty array
  if (b > 0)                        // if items in group great than 0
    for (;(d += b) < a.length;) {           // while index less than size of input array
      var s = a.slice(d, d + b);            // create group
      while(s.length < b)s.push(c||null);   // if size of group less than items in group - fill it with "fillWith"
      e.push(s);                            // add element to the result
    }
  return e
}

index.js

function(a,b,c,d,e){d=-b,e=[];if(b>0)for(;(d+=b)<a.length;){var s=a.slice(d,d+b);while(s.length<b)s.push(c||null);e.push(s)}return e}

LICENSE.txt

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

 Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE>

 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": "inGroupsOf",
  "description": "implementation of inGroupsOf function from prototype.js",
  "keywords": [
    "140bytes",
    "enumerable",
    "groups",
    "array",
    "prototype.js"
  ]
}