Which @angular/* package(s) are the source of the bug?

zone.js

Is this a regression?

No

Description

I publish an API whose primary interface is a frozen EventTarget. A customer reached out to me with an error originating from Angular Zone.js (reduced testcase & error noted below) that is interfering with use of this EventTarget.

It is clear that this library is attempting to store state in EventTarget instance fields. This does not follow best practices and is inadvisable as EventTarget instances can be frozen.

Please update zone.js/lib/common/events.ts to use private variables to store state instead of mutating public fields on EventTarget instances.

Please provide a link to a minimal reproduction of the bug

JS input:

Object.freeze(new EventTarget).addEventListener('test', () => { /* ... */ });

Please provide the exception or error you saw

Error:

Uncaught TypeError: Cannot add property __zone_symbol__testfalse, object is not extensible

Please provide the environment you discovered this bug in (run ng version)

N/A

Anything else?

Testcase:

let pass = true;
try {
  Object.freeze(new EventTarget).addEventListener('test', () => {})
} catch (ex) {
  pass = false;
}
console.log('EventTarget patcher is compatible with frozen EventTargets', pass)