map properties for arrays and objects

annotated.js

function(
  a, // source object or array
  b, // map function
  c, // (placeholder)
  d, // (placeholder)
  e  // (placeholder)
){
  c = a.length;  // get the length of the object.

  if (           // it's an array if
    c >= 0       // the length is zero or a positive integer,
  ) for (        // so loop by
    e = [],      // caching the target array,
    d = 0;       // initializing the cursor, and
    d < c;       // until the cursor reaches the length
    d++          // by increments,
  ) e[d] =       // push to the array
    b(a[d], d);  // the results of the map function
  
  else {         // otherwise, if the object has no length
    e = {};      // cache the target object, and
    for (        // for
      d          // each property
      in a       // in the source object
    ) e[d] =     // set the same on the target object with 
      b(a[d],d)  // the results of the map function
  }
  
  return e      // finally, return the target object
}

index.js

function(a,b,c,d,e){c=a.length;if(c>=0)for(e=[],d=0;d<c;d++)e[d]=b(a[d],d);else{e={};for(d in a)e[d]=b(a[d],d)}return e}

LICENSE.txt

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

 Copyright (C) 2011 Jed Schmidt <http://jed.is>

 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": "map",
  "keywords": ["map", "array", "arrays", "functional"]
}

test.js

// Define the map function
var map = function(a,b,c,d,e){c=a.length;if(c>=0)for(e=[],d=0;d<c;d++)e.push(b(a[d],d));else{e={};for(d in a)e[d]=b(a[d],d)}return e}

// Define an array and a object
var arr = ["a", "b", "c", "d", "e"]
var obj = {a:0, b:1, c:2, d:3, e:4}

// Map each, returing the key/val at each
arr = map( arr, function( value, index ){ return index + value } )
obj = map( obj, function( value, index ){ return index + value } )

// Log the results:
console.log( arr ) // => [ '0a', '1b', '2c', '3d', '4e' ]
console.log( obj ) // => { a: 'a0', b: 'b1', c: 'c2', d: 'd3', e: 'e4' }