Rationale behind supporting "Invalid Date"

Brendan Eich brendan at mozilla.com
Sat Feb 11 17:32:53 PST 2012

It's well-specified by etc.

This is all based on java.util.Date from ages ago, sorry it is painful. 
Have you considered wrapping Date with a user-defined function that 
throws if an invalid Date with a NaN time-value is created? Something 
like this:

var Date = function (origDate) {
   "use strict";
   return function Date() {
     if (!(this instanceof Date)) {
       // Approximate test for called-as-function, use apply.
       return origDate.apply(this, arguments);

     var args = [].slice.apply(arguments);
     var ctor = origDate.bind.apply(origDate, args);
     var date = new ctor;
     var time = date.getTime();
     if (time !== time) {
       throw 'Invalid Date';
     return date;


Andrew Paprocki wrote:
> I'm wondering if someone can point me to any past rationale for the
> decision to support Date objects in an "Invalid Date" state instead of
> throwing an exception whenever the user attempts to form an invalid
> date?
> Tracking down the source of script errors is difficult if something
> like "new Date(undefined)" is done, followed by a ".getTime()",
> propagating a NaN down layers of abstraction. Additional strange cases
> involve using NaN, Infinity, etc throughout the Date API.
> I was curious if there is a good reason for this or if potentially
> undefined / non-finite numbers could throw in a strict-mode setting. I
> didn't notice this behavior in the spec, but all browsers appear to
> follow the same convention.
> -Andrew
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss

More information about the es-discuss mailing list