A “true” Singleton approach would already initialized object, if it exists, or a new object, if it doesn’t. In the absense of AS3 style static variables, if you can dynamically add a property to the document, you could potentially use it to store a reference to the Singleton and then return that or a new object based on whether the object exists or not. It might look something like this:

function Singleton() {
if (document._myunlikelySingletonName) {
return document._myunlikelySingletonName;
} else {
var obj = new Object();
document._myunlikelySingletonName = obj;
return obj;
}

Of course, this presumes a slightly different purpose for wanting a Singleton–to make sure that everything referring to any instance of the Singleton is referring to the same thing. But like I said, you don’t need Singleton for the purpose of only ever having one instance created–you just create one instance!

I think if you find yourself in a case where you have an abnormally high number of calendars on a page, to the point where attaching listeners is affecting performance, you could always just change the clickhandling to listen to the parent container, and trigger from there.