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' }

Can't you get some savings here by using e[d]= instead of e.push() ?

good call, mike. fixed!

Hey, sorry for the piecemeal suggestions, but found another optimization... Now that you got rid of .push, instead of checking for e's type and doing either e = [], or e={},, you can just do e=a; after c=a.length to capture the appropriate type and then e[d]= will just overwrite the values. Saves another 6 bytes!

Woah, and then, if you do that, you can get rid of the if/else, and replace with ternary! Forking to test... brb.

Yeah, so for...in works on arrays too. Got this to be 58 bytes down from 121. :D https://gist.github.com/1012114 Not sure if this is cross-browser compatible or not, but I assume it would be

The array fork needs to check for sparse arrays and the object fork should check for own properties.