Optimize typing a single character

[Janpot]

What:

This improves performance of typing a single character by ~2x

Why:

Users complain about performance #577. Also related to this thread

How:

The desired behavior is to (I suppose) yield to the next macrotask in between keyboard actions. We can avoid the initial wait. Some quick benchmarking suggested those wait calls make up the bulk of the runtime of this function. When there is only 1 action to run, this brings the wait calls from 2 => 1

Checklist:

• Documentation
• Tests
• Ready to be merged
  

I don't believe documentation/tests would be required here.

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[ph-fritsche]

The initial wait ensures that micro tasks added during (re)render are done before we dispatch events or manipulate the DOM.

Could you verify that resolving the promise on a new event loop step carries that performance hit?
Or is this just caused by other tasks that run in between? Wouldn't these other tasks run afterwards if we remove the setTimeout call and result in about the same overall execution time?

[ph-fritsche]

This makes the function return Promise<undefined> instead of undefined for delay: null and results in await wait() to add a new micro task.
Are we sure this has no effect?

[Janpot]

Doesn't await wait() always create a new microtask regardless? Doesn't matter what wait() returns, right?

[ph-fritsche]

I'm not sure. I guess it depends on implementation.

Typescript reports 'await' has no effect on the type of this expression. ts(80007) if you try await undefined.

The following results in sync in node@10 and async in node@12:

async function waitAsync() {
    return undefined
}

function waitSync() {
    return undefined
}

(async function () {
    await Promise.race([
        (async () => {
            await waitAsync()
            return 'async'
        })(),
        (async () => {
            await waitSync()
            return 'sync'
        })(),
    ]).then(console.log)
})()

If we're not sure that this has no effect on any platform that is still supported, I wouldn't touch it if I don't have to.