Non-async resolve results in confusing behavior

[ArtskydJ]

I put some test data in the resolve, and forgot to set it as an async function. When I try to load a route, I don't get any error message or anything. It just appears to get stuck.

resolve: () => {
    const thing = {
        test_data: true
    }
    return thing
}

I would have expected it to either work as-is, or to throw an error about a missing .then method.

[TehShrike]

So ASR was originally written in the error-first callback style, and didn't support promises. Promise support was added later.

To maintain backwards compatibility, the callback style is still supported. The way that works is that if the resolve function returns a thenable, ASR internally resolves with the result of that thenable. Otherwise, it expects that the user plans to call the callback function in the future.

abstract-state-router/index.js

Lines 413 to 424 in 848dab9

	const resolves = Promise.all(statesWithResolveFunctions.map(state => new Promise((resolve, reject) => {
	const resolveCb = (err, content) => err ? reject(err) : resolve(content)
	resolveCb.redirect = (newStateName, parameters) => {
	reject(redirector(newStateName, parameters))
	}
	const res = state.resolve(state.data, parameters, resolveCb)
	if (isThenable(res)) {
	resolve(res)
	}
	})))

At this point I'm fine with publishing the breaking change that removes support for callback functions and only exposes the promise API. Callbacks have been dead for a long time.