stimulus-reflex:ready event should only be emitted once per page load

[leastbad]

Feature Request

Currently, the stimulus-reflex:ready event is emitted every time setupDeclarativeReflexes() is called. There are two concerns:

1. Someone might reasonably expect this to only be called once, leading to multiple initializations of app-level functions.
2. We might eventually remove the readystatechange handler in favour of just letting each Stimulus controller register itself... which means that calling the event when importmaps are in play could cause the event to fire before the controllers are actually ready.

Is your feature request related to a problem?

Ties into the solution provided by #606.

Describe the solution you'd like

The simple approach is to use a variable to track whether the event has been emitted, and then return if it's about to be emitted again. The complex approach - which I don't have a solution for due to my relative inexperience with importmaps - is to only emit the event when all controllers have registered. We don't currently have a mechanism to track this.

[marcoroth]

I don't think this should be a big deal, since we just exported that function a few commits ago in #602.

So it's never actually called twice unless you are explicitly importing the setupDeclarativeReflexes() function and calling it yourself in your application.

One solution might be to just move the emitEvent('stimulus-reflex:ready') to the eventlistener in javascript/stimulus_reflex.js:

document.addEventListener('readystatechange', () => {
  if (document.readyState === 'complete') {
    setupDeclarativeReflexes()
    emitEvent('stimulus-reflex:ready')
  }
})

[leastbad]

So it's never actually called twice unless you are explicitly importing the setupDeclarativeReflexes() function and calling it yourself in your application.

I don't believe that's correct. We call it every time the mutation observer picks up new elements.

stimulus_reflex/javascript/stimulus_reflex.js

Line 64 in 500e6c9

const observer = new MutationObserver(setupDeclarativeReflexes)

[marcoroth]

Oh, right. But that would mean that we were also emitting the event multiple times for a long time.

[leastbad]

Yes, stimulus-reflex:ready is a relatively recent addition. It's possible "very few" are using it, yet.