Frozen Date objects?

[Nathan Wall]

Erik Arvidsson wrote:
> This can either be done by exposing an object that has the same
> interface as Date. This could throw on set or it could skip the set
> methods entirely. If you want instanceof to work then all the methods
> needs to be overridden.

Overriding the methods on a real date object (or one that inherits from Date but was constructed with the Date constructor) won't work because then Date.prototype.set* methods would still be able to mutate the internal date by calling them explicitly:

    var readOnlyDate = getReadOnlyDate();
    readOnlyDate.setHours !== Date.prototype.setHours; // => true
    Date.prototype.setHours.call(readOnlyDate, 2); // oops

Also, I don't think `insanceof` should be used to check Dates. If Object.prototype.toString is used, the object just needs to be tagged as a "Date" and the function used to determine whether an object is a date needs to take into consideration "~Date" as well.

Nathan