📦 Bundle size

Full ESM build, minified and gzipped.

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

If you say there is no difference performance-wise, then I don't understand the motivation of this refactoring, tbh. If the current implementation works find and has no obvious flaws, I would not risk any sort of regression or unexpected behavior.

Basically this line motivated me to make this PR. Even though modern JavaScript engines seem to optimize this away, it's still not optimal for code that potentially runs very often. Switching to modern language features seemed like a safer bet in the long run ...and I was hoping for handleEvent support 😅

But I see your point; it's possible that users extend EventDispatcher and treat _listeners as public API, even though it shouldn't be. Feel free to close this.

Um, wouldn't reversing the loop order make the copy obsolete as well?

for ( let i = listenerArray.length - 1; i >= 0; i -- ) {

    listenerArray[ i ].call( this, event );

}

Good idea. I wasn't sure if this works so I tested it, but unfortunately it fails when multiple listeners are removed during dispatchEvent: https://jsfiddle.net/qc7avky9/3/

This would also obviously change the listener execution order which some users may (unknowingly) rely on.

There are probably more ways to get rid of the array copy in dispatchEvent, maybe with some two-layer approach: one working array and one iteration array with a dirty flag, but I like the simplicity of the map approach 😄