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events: allow dispatch many times without listener #39772

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events: allow dispatch many times without listener 
Fast path for EventTarget dispatch with no listeners didn't reset
kIsBeingDispatched flag, meaning same event couldn't be dispatched
multiple times.

Refs: #39395
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@mrbbot
mrbbot committed Aug 15, 2021
commit dd0146593cdad9fad37c85a8a04a6a6d9abd6f05
5 changes: 4 additions & 1 deletion lib/internal/event_target.js
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Original file line number Diff line number Diff line change
Expand Up @@ -422,8 +422,11 @@ class EventTarget {
}

const root = this[kEvents].get(type);
if (root === undefined || root.next === undefined)
if (root === undefined || root.next === undefined) {
if (event !== undefined)
event[kIsBeingDispatched] = false;
return true;
}

let handler = root.next;
let next;
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16 changes: 16 additions & 0 deletions test/parallel/test-eventtarget.js
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Expand Up @@ -186,6 +186,22 @@ let asyncTest = Promise.resolve();
deepStrictEqual(event.composedPath(), []);


eventTarget2.dispatchEvent(event);
strictEqual(event.eventPhase, Event.NONE);
strictEqual(event.target, eventTarget2);
deepStrictEqual(event.composedPath(), []);
}
{
// Same event dispatched multiple times, without listeners added.
const event = new Event('foo');
const eventTarget1 = new EventTarget();
const eventTarget2 = new EventTarget();

eventTarget1.dispatchEvent(event);
strictEqual(event.eventPhase, Event.NONE);
strictEqual(event.target, eventTarget1);
deepStrictEqual(event.composedPath(), []);

eventTarget2.dispatchEvent(event);
strictEqual(event.eventPhase, Event.NONE);
strictEqual(event.target, eventTarget2);
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