Make app.listen() return a promise

[felixfbecker]

Node's native listen() method takes a callback that gets executed once the server is ready. I expected the koa listen() to return a promise, but apparently it doesn't. This would be very helpful when setting up tests, for example in a mocha before hook, which understands promises:

describe('my app', function () {
  before(async function () {
    let app = koa()
    app.use(router)
    await app.listen()
  })
})

This example of course would also work without async/await by returning the promise.

[juliangruber]

you could just write your own lib that does return Promise(http.createServer(app.callback).listen) or something like that. There's no notion of Promise in koa yet and I assume other maintainers will agree that it's better to keep them out for now, at least until a new composing layer with async support lands.

[hallas]

what @juliangruber said

[tejasmanohar]

👍 for what @juliangruber said

[felixfbecker]

Yeah I do this now

Promise.promisifyAll(http.Server.prototype)
...
let server = http.createServer(app.callback())
await server.listenAsync()
...
await server.closeAsync()

This works, I'm just sick of promisifying everything. But maybe mz will add http one day.
But I must disagree with @juliangruber, there is a notion of promises in koa... Koa supports async functions as middleware, yielding of promises, ...
co moved to promises and I think koa should slowly move too, since async/await is definitly the future.
But this "small" change is really out of scope if I look at the tests and they rely on getting the httpServer from app.listen() everywhere.

[tejasmanohar]

@felixfbecker works w/ bluebird :)