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fix(ext/web): Copy EventTarget list before dispatch #19360

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merged 4 commits into from
Jun 5, 2023
Merged

fix(ext/web): Copy EventTarget list before dispatch #19360

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cd16b96
Copy EventTarget list before dispatch
Jun 4, 2023
ae73dd2
Added test, and double checking with [ci]
Jun 4, 2023
8bebe22
Change unnecessary let to const
vrugtehagel Jun 4, 2023
c3a721e
Keep performance optimization using suggestion
Jun 4, 2023
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14 changes: 14 additions & 0 deletions cli/tests/unit/event_target_test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -245,6 +245,20 @@ Deno.test(function eventTargetDispatchShouldSetTargetInListener() {
assertEquals(called, true);
});

Deno.test(function eventTargetDispatchShouldFireCurrentListenersOnly() {
const target = new EventTarget();
const event = new Event("foo");
let callCount = 0;
target.addEventListener("foo", () => {
++callCount;
target.addEventListener("foo", () => {
++callCount;
});
});
target.dispatchEvent(event);
assertEquals(callCount, 1);
});

Deno.test(function eventTargetAddEventListenerGlobalAbort() {
return new Promise((resolve) => {
const c = new AbortController();
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6 changes: 1 addition & 5 deletions ext/web/02_event.js
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Expand Up @@ -736,12 +736,8 @@ function innerInvokeEventListeners(
return found;
}

let handlers = targetListeners[type];

// Copy event listeners before iterating since the list can be modified during the iteration.
if (handlers.length > 1) {
handlers = ArrayPrototypeSlice(targetListeners[type]);
}
const handlers = ArrayPrototypeSlice(targetListeners[type]);
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I believe this was a useful optimization for us to keep our websocket perf up. Rather than reverting this and always cloning the array, I would suggest that we memoize the handlers.length instead so that in the case where we're not slicing the array, we'll only ever go through the loop once.

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Github won't allow me to added suggestions on deleted lines, but I think it would look like the code below:

  let handlers = targetListeners[type];
  const handlersLength = handlers.length;
  // Copy event listeners before iterating since the list can be modified during the iteration.
  if (handlersLength > 1) {
    handlers = ArrayPrototypeSlice(targetListeners[type]);
  }
  
for (let i = 0; i < handlersLength; i++) {

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Sounds good! Your suggestion has been committed 🙂


for (let i = 0; i < handlers.length; i++) {
const listener = handlers[i];
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