Add events.once

[browserify]

Add events.once

[vweevers]

You can pretty much copy https://github.com/nodejs/node/pull/26078/files, there have been no changes to the once function since that PR

[vvscode]

@goto-bus-stop as far as I see - there is already some .once implementation. And the existing one is incompatible with a new description

https://github.com/Gozala/events/blob/master/tests/once.js

[vweevers]

@vvscode That's require('events').EventEmitter.prototype.once, rather than require('events').once

[goto-bus-stop]

Yes, there is already a EventEmitter.prototype.once method that adds an event listener:

var emitter = new EventEmitter()
emitter.once('xyz', function (arg1, arg2) {
})

This is for the new EventEmitter.once method that returns a Promise instead:

var emitter = new EventEmitter()
var [arg1, arg2] = await EventEmitter.once(emitter, 'xyz')

[goto-bus-stop]

We don't have any build system for events.js. The tests are bundled using browserify but without babel or anything, so they should work in old browsers as much as possible (eg always use .then() instead of await).

The goal is to have identical behaviour to Node.js, so I think our tests should at least be based on Node's. they can be rewritten a bit (and have to be ported to older JS) but they should test the same functionality.

[goto-bus-stop]

@Doogiemuc hmm, I don't see it? that would break the entire ecosystem so I hope they wouldn't do that :)
There are two .once() functions: the long-time emitter.once(eventName, callback) method and the newer EventEmitter.once(emitter, eventName) associated function.

[vweevers]

It really should have gotten a distinct name 😄

[vvscode]

Ok. A frew more questions - don't you use any build system for https://github.com/Gozala/events/blob/master/events.js ?

Is it required copy-paste tests or I can write to them by myself?

[Doogiemuc]

Most recent version of NodeJS v12.10.0 changed the order of arguments for theoncemethod: https://nodejs.org/api/events.html