Events

by Julian Rubisch

Register Global Events in Your Markup

Bad 

connect() {
  document.addEventListener(...);
}

Good 

<div data-controller="gallery" data-action="resize@window->gallery#layout">...</div>


layout(e) {
  ...
}

Rationale

Stimulus will handle the adding and removing of event listeners.

Contraindications

The controller code makes assumption about the markup, which may not be feasible if you’re creating a Stimulus controller library. In this case, be sure to unregister your event listeners in disconnect.

Why does this happen?

A stimulus controller can connect / disconnect an arbitrary number of times. If eventListeners added in connect are not cleaned up on disconnect, you will have more than one eventListener for the given element and thus run your event listener callback multiple times instead of just once.

How to cleanup event listeners in connect / disconnect

Bad 

connect() {
  document.addEventListener("click", this.findFoo.bind(this))
}

disconnect() {
  document.removeEventListener("click", this.findFoo.bind(this))
}

findFoo() {
  console.log(this.element.querySelector("#foo"))
}

Good 

connect() {
  this.boundFindFoo = this.findFoo.bind(this)
  document.addEventListener("click", this.boundFindFoo)
}

disconnect() {
  document.removeEventListener("click", this.boundFindFoo)
}

findFoo() {
  console.log(this.element.querySelector("#foo"))
}

Why is the first one bad?

When you call .bind() on a function, it creates a new function. Therefore, calling bind twice means the add and remove eventListeners are calling different references of the function and the event wont be removed. Make sure that when adding and removing event listeners you use the same bound function reference.

Reference