Missing several format options

[schiem]

The Moment docs have a number of format options which are missing from DayJS. Some of them, like the locality specific ones, I think it makes sense to exclude, but there are others that are missing that could be included without having a serious impact on the library size.

Here are the missing formats that I propose are added:

• Q - Quarter of the year
• Do - Day of month with ordinal
• DDD/DDDD - Day of year
• X - Unix timestamp
• x - Unix timestamp with ms
• h/hh - 12 hour time
• k/kk - 24 hour time beginning at 1
• a/A - Post and ante meridiem
• S/SS/SSS - Milliseconds

However, this would nearly double the size of the format function, which isn't ideal. Are there any of those that shouldn't be added?

[Frondor]

In my humble opinion, the only useful ones in that list are h/hh and k/kk (and still not sure about them, can't think on an use case). The rest doesn't look like human-friendly formats.

[schiem]

I would tend to agree, I think that Q, DDD/DDDD, X/x, and S/SS/SSS are definitely not necessary. I think if h/hh is included, then a/A should probably be included as well, or you lose the ability to show specific times (1:00 vs 1:00 AM).

"Do" is kind of up in the air for me, because I've had clients who've insisted on having the ordinal (1st, 2nd, 3rd, etc) shown, but it's something that a user could implement on their own. I think most of it comes down to "what should be provided by a library" vs. "what can a user be reasonably expected to write themselves," and I think that's mostly up to the owner of the repo.

[iamkun]

I tend to agree adding h/hh & a/A(with local). And leave the rest formats to a separate plugin, maybe called AdvFormat
It will be nice if we implement a plugin system like this.

import { AdvFormat } from 'dayjs/plugin'
dayjs.extend('AdvFormat') // a plugin might add a new API or overwrite the existing one
//here it just overwrite the core.format
dayjs.format('Do SSS ... something less useful format')

[schiem]

I've updated #68 to only have AM/PM and 12 hour time support, with additional options included in another plugin (and the addition of a plugin system).

[schiem]

The PR from #68 has been split into #91 and #92.