toLocaleDateString() results in "Method invoked on an object that is not Date" error in Chrome

[TylerRick]

After calling Timecop.install and Timecop.travel, when I then call toLocaleDateString() on any date object, I get this error:

(new Date).toLocaleDateString()
TypeError: Method invoked on an object that is not Date.

(new Date).toLocaleTimeString()
TypeError: Method invoked on an object that is not Date.

The backtrace is:

toLocaleDateTime v8/i18n:1107
Object.defineProperty.value v8/i18n:1132
Timecop.MockDate.(anonymous function) timecop.js:173

You can where the error is defined in the V8 source code here:

function toLocaleDateTime(date, locales, options, required, defaults, service) {
  if (!(date instanceof Date)) {
    throw new TypeError('Method invoked on an object that is not Date.');
  }
  ...

I don't understand it completely, but it looks like even though we called the toLocaleDateTime method on an actual native Date object (this._underlyingDate), the way toLocaleDateTime is defined (Object.defineProperty(Date.prototype, 'toLocaleDateString',...), it ends up calling toLocaleDateTime with a non-native Date object (presumably a Timecop.MockDate object) as the first argument. Hence my proposed workaround in the attached pull request...

I'm using Chromium Version 28.0.1500.52 Ubuntu 12.04 (28.0.1500.52-0ubuntu1.12.04.2).

[jamesarosen]

I don't see this problem in a simplistic reduction:

function MockDate(date) {
  this._underlyingDate = date || new Date();
}

MockDate.prototype.toLocaleDateString = function() {
  return this._underlyingDate.toLocaleDateString.apply(this._underlyingDate, arguments);
}

d1 = new MockDate()
d2 = new MockDate(d1)
d2.toLocaleDateString()
"7/16/2013"

That suggests that something else is going wrong.

[TylerRick]

You might be right. I pasted your simplistic MockDate into the console of my Chrome browser and it worked fine.

I guess I should find a minimal reproduction of the bug first. Don't have time at the moment though...

[jamesarosen]

I'll leave this open for a while. It sounds somewhat serious, so if we can find a test case, I'd like to solve it.