postMessage detector

ba-postMessage-detect.js

/*!
 * postMessage detector - v0.1pre - 9/15/2010
 * http://benalman.com/
 * 
 * Copyright (c) 2010 "Cowboy" Ben Alman
 * Dual licensed under the MIT and GPL licenses.
 * http://benalman.com/about/license/
 */

// If `window.postMessage.complex` is true, postMessage can pass complex non-string
// values like objects and arrays. If it's false, it can only pass strings (TODO: test)
// 
// Note that since postMessage executes asynchronously, this value isn't available
// immediately... Ugh.

(function(window,message,postMessage){
  
  var tmp,
    timeout_id = setTimeout(function(){
      handler({});
    },1);
  
  function handler(e){
    clearTimeout( timeout_id );
    
    tmp = e.data;
    if ( window.postMessage ) {
      window.postMessage.complex = tmp && typeof tmp != 'string' && tmp.t;
    }
    
    if ( tmp = window.removeEventListener ) {
      tmp( message, handler, false );
    } else if ( tmp = window.detachEvent ) {
      tmp( 'on' + message, handler );
    }
  };
  
  if ( postMessage in window ) {
    
    if ( tmp = window.addEventListener ) {
      tmp( message, handler, false );
    } else if ( tmp = window.attachEvent ) {
      tmp( 'on' + message, handler );
    }
    
    window[ postMessage ]( { t: true }, '*' );
  }
  
})(this,'message','postMessage');

// Usage
setTimeout(function(){
  alert([
    'window.postMessage: ' + !!window.postMessage,
    'window.postMessage.complex: ' + ( window.postMessage && window.postMessage.complex )
  ].join('\n'))
}, 100)

why does this need to be async? remember why the setTimeout?