[Jeremen]

Deff, понятно.
Вот нагуглил "onDomReady без jQuery". Исходный код взят с jQuery.

(function(){
  var readyBound = false;
  var bindReady=function(){
    if ( readyBound ) return;
    readyBound = true;
    if ( document.addEventListener ) {
        document.addEventListener( "DOMContentLoaded", function(){
          document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
          ready();
        }, false );
    } else if ( document.attachEvent ) {
      document.attachEvent("onreadystatechange", function(){
        if ( document.readyState === "complete" ) {
          document.detachEvent( "onreadystatechange", arguments.callee );
          ready();
        }
      });
      if ( document.documentElement.doScroll && window == window.top ) (function(){
        if ( isReady ) return;
        try {
          document.documentElement.doScroll("left");
        } catch( error ) {
          setTimeout( arguments.callee, 0 );
          return;
        }
        ready();
      })();
    }
    if (window.addEventListener)
      window.addEventListener('load', ready, false);
    else if (window.attachEvent)
      window.attachEvent('onload', ready);
    else
      window.onload=ready;
  }
  var isReady=false
  var readyList= [];
  var ready=function() {
    if ( !isReady ) {
      isReady = true;
      if ( readyList ) {
        var fn_temp=null
        while(fn_temp=readyList.shift()){
          fn_temp.call( document);
        }
        readyList = null;
      }
    }
  }
  domReady=function(fn) {
    bindReady();
    if ( isReady )
      fn.call(document);
    else
     readyList.push( fn );
     return this;
  }
})();