Simplest/Cleanest way to implement singleton in JavaScript?

Question

What is the simplest/cleanest way to implement singleton pattern in JavaScript?

Answer 1

I deprecate my answer, see my other one.

Usually module pattern (see CMS' answer) which is NOT singleton pattern is good enough. However one of the features of singleton is that its initialization is delayed till object is needed. Module pattern lacks this feature.

My proposition (CoffeeScript):

window.singleton = (initializer) ->
  instance = undefined
  () ->
    return instance unless instance is undefined
    instance = initializer()

Which compiled to this in JavaScript:

window.singleton = function(initializer) {
    var instance;
    instance = void 0;
    return function() {
        if (instance !== void 0) {
            return instance;
        }
        return instance = initializer();
    };
};

Then I can do following:

window.iAmSingleton = singleton(function() {
    /* This function should create and initialize singleton. */
    alert("creating");
    return {property1: 'value1', property2: 'value2'};
});


alert(window.iAmSingleton().property2); // "creating" will pop up; then "value2" will pop up
alert(window.iAmSingleton().property2); // "value2" will pop up but "creating" will not
window.iAmSingleton().property2 = 'new value';
alert(window.iAmSingleton().property2); // "new value" will pop up