Load javascript async, then check DOM loaded before executing callback

Question

Problem:
Load js files asynchronously, then check to see if the dom is loaded before the callback from loading the files is executed.

Answer 1

You can always put your initial loader script at the bottom, right before the closing body tag.

Answer 2

What you need is a simple queue of onload functions. Also please avoid browser sniffing as it is unstable and not future proof. For full source code see the [Demo]

var onload_queue = [];
var dom_loaded = false;

function loadScriptAsync(src, callback) {
  var script = document.createElement('script'); 
  script.type = "text/javascript";
  script.async = true;
  script.src = src;
  script.onload = script.onreadystatechange = function() {
    if (dom_loaded) 
      callback();
    else 
      onload_queue.push(callback);
    // clean up for IE and Opera
    script.onload = null;
    script.onreadystatechange = null;
  };
  var head = document.getElementsByTagName('head')[0];
  head.appendChild(script);
}

function domLoaded() {
   dom_loaded = true;
   var len = onload_queue.length;
   for (var i = 0; i < len; i++) {
     onload_queue[i]();
   }
   onload_queue = null;
};

// Dean's dom:loaded code goes here
// do stuff
domLoaded();

Test usage

loadScriptAsync(
  "http://code.jquery.com/jquery-1.4.4.js", 
  function() {
      alert("script has been loaded");
   }
);