JavaScript Spec Change on Date Time Zone Default

JavaScript spec changed on its datetime string format in 2015.

when you have a date string missing the time zone, example:

(new Date("2014-12-31T23:08")).getHours()

what is the assumed time zone?

• ECMA-262 5.1 edition, June 2011 says it should assume Z
• ECMA-262, 6th edition, June 2015 says it should assume local time.

As of 2015-04-11, 2016-04-26, 2016-12-13,

(new Date("2014-12-31T23:08")).getHours()

, Firefox returns 23 (which is assuming local time), Chrome assumes Z and returns 15 or other value.

As of 2022-07-28, chrome, Firefox, all assume local time.

console.log( (new Date("2014-12-31T23:08")).getHours() );