fix: ensure event delegation stops after an error

[dummdidumm]

When a delegated event handler throws an error, ensure that delegated event handlers above it don't run. Strictly speaking this is different from attaching multiple separate event listeners because those above would still run, but it's impossible for us to simulate this behavior here. Fixes #8403

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[Rich-Harris]

Surely we want handlers higher up in the tree to run normally? Errors shouldn't stop propagation. In #8403 (comment), the weirdness I was referring to was that the 'nope' error was logged twice when you hit the first button, instead of behaving the same as the second button (notwithstanding that the second button also behaves weirdly after the first click). I'd expect both buttons to result in one 'nope' error followed by a 'hello'.

(This would technically be a breaking change since this is also broken in Svelte 4.)

[dummdidumm]

But how do you want to do that? The traversal upwards is synchronous, and not throwing an error (instead a console.error) would not be the same, wouldn't it?

[Rich-Harris]

I think you can do it by recursing inside a finally block:

function nope() {
  throw new Error('nope');
}

function yep() {
  console.log('hello');
}

function go(handlers, i = 0) {
  try {
    handlers[i]();
  } finally {
    if (++i < handlers.length) {
      go(handlers, i);
    }
  }
}

go([nope, yep]);

[Rich-Harris]

opened #11263 as an alternative

[Rich-Harris]

merged #11263 — closing