Can 'this' be undefined from within a prototype function?

Question

Is it possible for this prototype function to return false or is it a pointless check that will always return true?

if (!Date.prototype.hasOwnProperty("foo")) {
    Date.prototype.foo = function () {
        var date = this;
        if (!date) {
            return false;
        }
        return true;
    }
}

Answer 1

The this keyword in JavaScript is only undefined if strict mode is enabled. Otherwise, it will reference the window object by default, unless any of the following are true:

• The function is called using the new operator
• A different object is bound to this using call() or apply()