`onbeforeremove` should tolerate thenables that synchronously resolve

[dead-claudia]

Mithril version: v2.0.4 (not new, though)

Browser and OS: All

Project:

Code

const Comp = {
	view: () => m("div"),
	onbeforeremove: () => {
		then(resolve, reject) {
			resolve(delay(100))
		},
	},
}

function delay(ms) {
	return new Promise(resolve => { setTimeout(resolve, ms) })
}

Steps to Reproduce

Expected Behavior

It to operate asynchronously

Current Behavior

It doesn't wait.

Context

We're not honoring the Promises/A+ spec here. And fixing this is as simple as changing these two lines to wrap their this value with Promise.resolve(...).

[kfule]

Currently, mithril uses finally() instead of then() to handle onbeforeremove, so a simple thenable object seems to cause an error. (flems)
(Implementing finally() in thenable objects reproduces the not-waiting problem as described. (flems) This is no longer a proper test code, though.)

Anyway, it seems to me that wrapping the stateResult and attrsResult in Promise.resolve() would be a good solution.