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 "scripts", 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 0 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

Copyright (c) 2011 Jed Schmidt, http://jed.is
 
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
 
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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 :)