Incompatibility with datejs

[jpettitt]

Not really an express bug. Opening issue here for the sake of others wondering why their code broke.

If you install datejs it modifies the stock Date.parse() function to handle more date formats. Unfortunately it now returns null instead of NaN and that breaks conditional request handling in express.static causing spurious 412 errors.

datejs Issue abritinthebay/datejs#263

[dougwilson]

Weird for sure. Not sure if anything can be done there, since there is the potential for anything to overwrite the global Date object to anything. It's hard to program it to assume the entire environment can't be trusted to conform to the spec...

[dougwilson]

There have been a few more issues related to this, all traced back to this datejs issue. I'm gearing up a 1.15.1 release to include a work-around.

[dougwilson]

So there is yet another issue with datejs: the Date.parse it overrides in the environment not only incorrectly returns null instead of NaN, it also returns an instanceof Date instead of a plain number when it succeeds... see conversation in pillarjs/send#130 (comment)