Configure the timezone that is assumed by parsing methods

[Azmisov]

When a user doesn't provide a timezone in a string, I would like to assume GMT/UTC timezone. Currently, if a timezone is not provided, it is assuming my local computer's timezone. For example (my computer is set to MST timezone):

let gmt = Date.parse("1/1/2017 10:45 GMT");
let mst = Date.parse("1/1/2017 3:45 MST");
let assume = Date.parse("1/1/2017 3:45);

console.log(+gmt == +mst); // true
console.log(+assume == +mst); // true, since my computer is in MST timezone

Can we add an argument to Date.parse to supply the UTC offset to assume, rather than using the computer's local timezone? This is the behavior I would expect:

let mst = Date.parse("1/1/2017 3:45 MST", "+0000");
let explicit = Date.parse("1/1/2017 10:45", "+0000");

console.log(+explicit == +mst); // should be true

[abritinthebay]

Easiest way to do that is to add the offset to the string (if one doesn't exist). Dates in JS are always local to the host computer. This will be true even if you set the offset (it'll return the date in the local timezone just modified so it's accurate if it was the time you wanted.

So without a major overhaul of JS date parsing the solution is "append the tz to your data"

[Azmisov]

Any suggestions on detecting whether an offset exists on the string already? I can't append it unconditionally, since DateJS parser seems to use that, instead of any previously defined offsets. Seems like I'm going to have to write my own complicated date parser, just to do that.

But doesn't DateJS's parser extract the offset and apply it already? Seems like it would be very simple just to add an override to that. That wouldn't be a major overhaul at all. Just something like:

Date.parse = function(str, assumed_offset){
    ...
    let offset = DateJSParser.parsed_offset || assumed_offset;
    if (offset)
        applyOffset(offset, ...);
    ...

[abritinthebay]

You're asking for a chain modifier - so chain modify it yourself?

Date.parse(string).addHour(offsetAmount) does exactly what you're requesting above.

[Azmisov]

But I want to add the offset only conditionally. Currently, there is no API to detect if the parser applied a user-defined offset. Example:

let has_user_offset= Date.parse("1/1/17 3:00 MST");
let no_user_offset = Date.parse("1/1/17 3:00");

How would I detect that the parser has added a 7 hour offset to has_user_offset and not to no_user_offset?

I mean, if you guys don't want to implement this that's fine. Its just a suggestion to help improve the library. I suppose I'll just have a separate select box for specifying a timezone, and then maybe use MomentJS's UTC parsing mode.

[abritinthebay]

It's not going to be a priority either way. What you're describing with MomentJS can be done with existing DateJS functions btw so I refer you to my previous solution.

That said - if you absolutely want it then PRs are welcome.