You're mostly fine, you can directly access globalVar from any script running anywhere in the page if you declare it the way you have.
Specifically: Using var x; at page-level scope (that is, outside of any function) declares a property on the window object (it has a special feature in that it can't be deleted, but that's not important here).
var foo = 2;
window.foo = 2; // Basically the same other than the delete thing we're not worrying about here
And so:
var foo = 2;
alert(foo); // alerts "2"
alert(window.foo); // also alerts "2"
window.bar = 4;
alert(window.bar); // alerts "4"
alert(bar); // also alerts "4"
Naturally this is only true at the top level, outside of any functions. Inside functions, you're declaring something local to the function. (In essence; it's actually a lot more interesting than that.)
But since you've asked about scope, it's worth nothing that all of the other things you've defined (initialize, getTheVar, doSomething) are also globals. In general, you want to avoid putting anything in the global namespace that you can avoid putting there.
For that reason, I advocate always using a "scoping function":
(function() {
// your code here
})();
...and explicitly exporting exactly and only the things you really need to be global (by assigning them to properties on window).
In your case, you've said you need globalVar and you've also used initialize (although there are other ways to do what you're doing in initialize), so you could do this:
(function() {
var globalvar;
// Exports
window.globalVar = globalVar;
window.initialize = initialize;
// Implementation
function initialize() {
var someVariable = 5;
doSomething(someVariable, getTheVar);
}
function doSomething(someVariable, expectGlobalVar) {
//alert(someVariable);
alert(expectGlobalVar);
}
function getTheVar() {
globalVar = "test";
return globalVar;
}
})();
But you can take it further. Since you're not calling initialize until the load event of the body element, you could avoid publishing initialize. Just put your script tag at the end of the document, just before the closing </body> tag (as the YUI folks recommend), and do your initialization there:
<html>
<head>
<title>...</title>
</head>
<body>This is a test
<script type='text/javascript'>
(function() {
var globalvar;
// Initialization
initialize();
// Exports
window.globalVar = globalVar;
// Implementation
function initialize() {
var someVariable = 5;
doSomething(someVariable, getTheVar);
}
function doSomething(someVariable, expectGlobalVar) {
//alert(someVariable);
alert(expectGlobalVar);
}
function getTheVar() {
globalVar = "test";
return globalVar;
}
})();
</script>
</body>
</html>
The DOM is fully loaded and ready to go at that point.
But we can go even further if we want: We can have nothing in the global namespace if we like. If you hook up all of your handlers within your initialize function rather than using onload, onclick, and similar attributes, there's no need for globalVar to be global except to your code. (You hook up handlers after the fact by using attachEvent [on IE], addEventListener [on standards-based browsers], or better yet using a library like jQuery, Closure, Prototype, YUI, or any of several others.)