communicate with jsonp

annotated.js

function e(
  a, // the url, such as "http://test.com/foo?q=bar&callback="
  b, // the callback function
  c, // placeholder
  d  // placeholder
){
  with (document) body // on the document body,
    .appendChild(      // attach
      createElement(   // a created script.
        d = "script"   // set d to "script", used later as prefix
      )
    )
    .src = a + (  // set src to url +
      c = d + (   // the name on the window, which is "script" +
        e.a =     // the current increment, which is
          -~e.a   // itself + 1, coercing to 1 if not yet defined,
      )
    );

  (a=window)[c] = function(d) { // put the callback on the window object, and
    a[c] = b(d)                 // call/clear it when it's done.
  }
}

index.js

function e(a,b,c,d){with(document)body.appendChild(createElement(d="script")).src=a+(c=d+(e.a=-~e.a));(a=window)[c]=function(d){a[c]=b(d)}}

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": "jsonp",
  "keywords": ["jsonp", "AJAX", "communication", "get"]
}

Naming the function here breaks the rules of not polluting global scope. Only function expressions are allowed. Wrapping it in parentheses will make it a function expression.

It only pollutes if it's included as is, and not as part of a statement. This will be more clear when I make the API official.

Hat tip to @arlolra, whose idea to coerce using ~ ended up saving three bytes, allowing use of the safer window instead of this.

use => arrow fn instead :)