Get the given date format (the string specifying the format) in javascript or momentjs

Question

Given a datestring, how can I get the format string describing that datestring?

Put another way, how can I get the format string that Date() or MomentJS (might be di

Answer 1

You can't, without having additional information, such as the locale. For example, 01/12/16 could be Jan 12, 2016, December 1, 2016, or December 16, 2001.

Even when you know the locale, there are several places in the real world where more than one date format is used, depending on context.

See https://en.wikipedia.org/wiki/Date_format_by_country

However, if you are just trying to determine which one of multiple known formats was used to parse the input string, moment has an API for that called Creation Data. For example:

var m = moment("2016/06/10", ["YYYY-MM-DD", "MM/DD/YYYY"], true);
var f = m.creationData().format;  // "MM/DD/YYYY"

Answer 2

Consolidating information from Matt Johnson's answer, some comments, and my own contribution.

With Moment.js (version 2.10.7+), you can use the Creation Data API. Something like this in Node.js:

moment('2016-01-01 00:00:00').creationData().format

outputs

'YYYY-MM-DD HH:mm:ss'

Just as any date parsing is, there is ambiguity about the format of many datestrings due to things such as locale (the order of months and days are switched between the US and Europe, for example). But the above method is sufficient for me.