I want to perform asynchronous JavaScript downloads of two files that have dependencies attached to them.

// asynch download of jquery and gmaps
function addScript(url) {
    var script = document.createElement('script');
    script.src = url;
    document.getElementsByTagName('head')[0].appendChild(script);
}
addScript('http://google.com/gmaps.js');
addScript('http://jquery.com/jquery.js');

// define some function dependecies
function requiresJQuery() { ... }
function requiresGmaps() { ... }
function requiresBothJQueryGmaps() { ... }

// do some work that has no dependencies on either JQuery or Google maps
...

// QUESTION - Pseudo code below
// now call a function that requires Gmaps to be loaded
if (GmapsIsLoaded) { requiresGmaps(); }

// QUESTION - Pseudo code below
// then do something that requires both JQuery & Gmaps (or wait until they are loaded)
if (JQueryAndGmapsIsLoaded) { requiresBothJQueryGmaps(); }

Question: How can I create an event to indicate when:

• JQuery is loaded?
• Google Maps is loaded
• JQuery & Google Maps are both loaded?