Bug 289337 – REGRESSION (285042@main-285687@main): `RegExp["$&"]` incorrectly returns an empty string

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[RiskyMH]

`RegExp["$&"]` should return the last matched substring but now returns an empty string when using `.match(/bar/g)`. However, it works if the match includes a capturing group.


```js
"foo bar baz".match(/bar/g);
console.log([RegExp["$&"]]);  // Expected: ["bar"], Current: [""]

"foo bar baz".match(/ba(r)/g);
console.log([RegExp["$&"]]);  // Expected and Current: ["bar"]
```

Observed Behavior:

- Broke between WebKit commits `96471cc` and `1b53bfc`
- See bun's fork diff https://github.com/oven-sh/WebKit/compare/543cca2...9b84f43 (bun `1.1.33..1.1.34`)

Possible Cause: https://commits.webkit.org/285090@main

---

reported on Bun's repo https://github.com/oven-sh/bun/issues/17978

[Radar WebKit Bug Importer]

<rdar://problem/146622507>

[Yusuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/42177

[EWS]

Committed 291881@main (cc0a0f907148): <https://commits.webkit.org/291881@main>

Reviewed commits have been landed. Closing PR #42177 and removing active labels.

[EWS]

Committed 289651.257@safari-7621-branch (90e15f4a2340): <https://commits.webkit.org/289651.257@safari-7621-branch>

Reviewed commits have been landed. Closing PR #2776 and removing active labels.