inheritance - How to extend the Javascript Date object?

Question

I'm trying to subclass/extend the native Date object, without modifying the native object itself.

I've tried this:

    var util = require('util');

    function MyDate() {
        Date.call(this);
    }
    util.inherits(MyDate, Date);

    MyDate.prototype.doSomething = function() {
        console.log('Doing something...');
    };        

    var date = new MyDate();
    date.doSomething();

    console.log(date);
    console.log(date.getHours());

and this:

function MyDate() {

    }

    MyDate.prototype = new Date();

    MyDate.prototype.doSomething = function() {
        console.log("DO");
    }

    var date = new MyDate();
    date.doSomething();
    console.log(date);

In both cases, the date.doSomething() works, but when I call any of the native methods such as date.getHours() or even console.log(date), I get 'TypeError: this is not a Date object.'

Any ideas? Or am I stuck to extending the top-level Date object?

Answer 1

Looking at the v8 code, in date.js:

function DateGetHours() {
  var t = DATE_VALUE(this);
  if (NUMBER_IS_NAN(t)) return t;
  return HOUR_FROM_TIME(LocalTimeNoCheck(t));
}

And looks like DATE_VALUE is a macro that does this:

DATE_VALUE(arg) = (%_ClassOf(arg) === 'Date' ? %_ValueOf(arg) : ThrowDateTypeError());

So, seems like v8 won't let you subclass Date.