Javascript DOM Ready

If you want to reproduce the jQuery's document.ready event, you can use the onreadystatechange or DOMContentLoaded events where applicable:

function domReady () {
  document.body.className += " javascript";
  // ...
}

// Mozilla, Opera, Webkit 
if ( document.addEventListener ) {
  document.addEventListener( "DOMContentLoaded", function(){
    document.removeEventListener( "DOMContentLoaded", arguments.callee, false);
    domReady();
  }, false );

// If IE event model is used
} else if ( document.attachEvent ) {
  // ensure firing before onload
  document.attachEvent("onreadystatechange", function(){
    if ( document.readyState === "complete" ) {
      document.detachEvent( "onreadystatechange", arguments.callee );
      domReady();
    }
  });
}

Cross-browser fallback

Internet Explorer 8 supports the readystatechange event, which can be used to detect that the DOM is ready. In earlier version of Internet Explorer, this state can be detected by regularily trying to execute document.documentElement.doScroll("left");, as this snippet will throw an error until the DOM is ready.

https://developer.mozilla.org/en-US/docs/Web/Reference/Events/DOMContentLoaded