Date constructor: numeric arguments vs. string argument giving different dates in some cases

Question

First of all, I think timezone probably has something to do with this. I\'m in EST/EDT. Also, I\'m testing this on chromium 17 / linux.

Now, let\'s say I create two

Answer 1

It looks like the date constructor requires spaces rather than '-'. Its the recommended way. Check out this link:
3.3. Date and Time Specification

Though foldingwhite space is permitted throughout the date-time specification, it is RECOMMENDED that a single space be used in each place that FWS appears (whether it is required or optional)

Also check out this link:
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date

dateString: String value representing a date. The string should be in a format recognized by the parse method (IETF-compliant RFC 2822 timestamps).

I tried following code and it returns true

dateFromNumbers = new Date(2020, 11, 15);
dateFromString = new Date("2020 12 15");
alert(+dateFromNumbers == +dateFromString);​

Also its not a problem start with the month of October, it has do with the double digit months. If I try the same method with September then:

dateFromNumbers = new Date(2020, 8, 15);
dateFromString = new Date("2020-09-15");
alert(+dateFromNumbers == +dateFromString);​ // This returns false

But if I use single digit for September then it returns true

dateFromNumbers = new Date(2020, 8, 15);
dateFromString = new Date("2020-9-15");
alert(+dateFromNumbers == +dateFromString);​ // This returns true

And if use space with double digit September, then it returns true

dateFromNumbers = new Date(2020, 8, 15);
dateFromString = new Date("2020 09 15");
alert(+dateFromNumbers == +dateFromString);​//This returns true