make Popper#update sync + make scheduleUpdate return promise

CodePen Demo

https://codepen.io/anon/pen/NwZQwK

What is the expected behavior?

In the CodePen, the popper should incorrectly be positioned if the update was sync. But because it’s not, the last transform line is what Popper knows about, not the first one.

Any other comments?

The asynchronous popper.update() can cause some issues if the next line of code assumes the popper’s position has been updated. The onUpdate() callback can’t really be used depending on the code structure.

I’ve been able to remedy this for a while with setTimeout() defer calls (not sure if this is 100% reliable though), but it would be easier just to have a sync update method.

That, or update is sync while scheduleUpdate is async.

Is there a case where this wouldn’t be appropriate?

[bimbiltu]

Hey @FezVrasta im writing a library that uses popper but I cannot assume that the environment my code runs in will support Promises. How do you feel about scheduleUpdate supporting both callbacks and Promises, similar to Vue’s $nextTick. The code could look like:

function scheduleUpdate(cb) {
  requestAnimationFrame(() => this.debouncedUpdate(cb || () => {}));
  if (!cb && typeof Promise !== 'undefined') {
    return new Promise(resolve => cb = resolve);
  }
}

Id be happy to submit a PR with this code and tests to along with it

[FezVrasta]

Wow cool, good to know.

I think we can plan this change in the next major version, along with a promise-based API for scheduleUpdate.