MutationObserver disconnect fails if no elements are observed

[spudly]

Describe the bug
If you call disconnect() on a MutationObserver instance that is not yet observing any elements, it will fail with this error: TypeError: Cannot read properties of null (reading '_unobserve')

To Reproduce

import {Window} from 'happy-dom';

const window = new Window();

const observer = new window.MutationObserver(() => {});
observer.disconnect();

Expected behavior

No error

Screenshots

n/a

Device:

• OS: MacOS
• Browser: N/A (NodeJS / Jest / @happy-dom/jest-environment)
• Version [e.g. 22]

Additional context

The bug is here: https://github.com/capricorn86/happy-dom/blob/master/packages/happy-dom/src/mutation-observer/MutationObserver.ts#L58

this.target is null until observe() is called, so if you call disconnect before that, it throws the error. I think it should probably be looping over a list (WeakSet?) of observed elements and calling _unobserve on each one.

[capricorn86]

Thank you for reporting @spudly! 🙂

Big thanks to @victorwedo for making a fix! ⭐

The fix has now been released.

You can read more about the release here:
https://github.com/capricorn86/happy-dom/releases/tag/v8.2.2