Prevent object constructor being run as function

Great point. How about warning and redirecting to new Foo() instead of throwing an exception?

function Foo() {
 // verify the new operator was used to
 // ensure 'this' works as expected
 if (false === (this instanceof Foo)) {
 console.warn('Foo() invoked as a function;',
 'use `new Foo()` instead');
 return new Foo(arguments);
 }
 // ...
}

Good idea. I'm building new things at the moment, so I wanted other coders to know if they're doing something wrong before it can become a bug later, but if you're adding into existing code it'd make sense to be a warning rather than crash the entire suite. Thanks :)

Perfect, simple and easily implemented on existing code.

Isn't this essentially describing a singleton pattern? http://addyosmani.com/resources/essentialjsdesignpatterns/book/#singletonpatternjavascript