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Derived class that calls super() then returns a Proxy trips "Must call super constructor" — blocks node-fetch after #10759 #10809
Description
With #10759 fixed (PR #10807), node-fetch@3.3.2 gets past the Function.prototype.call was called on a value that is not a function failure and hits the next one:
ReferenceError: Must call super constructor in derived class before accessing 'this'
or returning from derived constructor
raised inside node-fetch's real Headers.js. Pre-existing and separate from #10759 — reported rather than fixed, per that task's scope.
The shape
node-fetch's Headers is a derived class whose constructor calls super(...) and then returns a Proxy wrapping this:
export default class Headers extends URLSearchParams {
constructor(init) {
// ...normalise init into `result`...
super(result);
return new Proxy(this, { get(target, p, receiver) { /* ... */ } });
}
}That is legal JavaScript and Node executes it without complaint. Perry raises the derived-constructor guard anyway.
Worth noting the guard is doing its job in general — this is not a claim that the check is wrong, but that something in this shape (a super() call followed by a constructor-return override, with a Proxy as the returned value) is not being recognised as having satisfied it.
Why it is worth attention beyond node-fetch
The constructor-return-override is not exotic. Returning a Proxy from a constructor is the standard way to give a class a dynamic property surface, and doing it from a derived class — after super() — is exactly what a subclass of a builtin must do. Anything wrapping a builtin this way is a candidate.
Reproduction
mkdir nf-probe && cd nf-probe
npm install node-fetch@3.3.2
# package.json: { "perry": { "compilePackages": ["node-fetch"] } }
# fixture.ts: import fetch from "node-fetch"; then a GET against a local node:http server
perry compile fixture.ts -o fixture && ./fixtureA package-independent reduction is the obvious first step and was not attempted: a derived class extending a builtin, calling super(), then returning new Proxy(this, {...}). If that reproduces, node-fetch is incidental.
Status
This is the second distinct defect in node-fetch's path, after #10759. Real-source node-fetch remains blocked, and its binding should not be removed until this is resolved. #10759's fix is correct and complete for what it claims — its gap test covers the same derived-class-plus-Proxy shape and passes byte-for-byte against Node — but the package needs both.
Activity
proggeramlug commentedon Sep 21, 2026
Re-tested this against current
main(47ade47327) with the realnode-fetch@3.3.2source graph (22 compiled modules:node-fetch,data-uri-to-buffer,fetch-blob,formdata-polyfill,node-domexception, andweb-streams-polyfill).The reported derived-constructor failure is no longer reproducible:
Headersgets throughsuper(...)and its Proxy return without theMust call super constructorerror. The existingtest_gap_10759_urlsearchparams_prototype_method_value.tsreduction also passes.The full local-HTTP fixture now reaches a later, separate HTTP integration failure:
This result establishes only that the original symptom does not reproduce on current
main; the cause of the difference from the earlier run is unknown. The current node-fetch blocker is tracked separately in #10887.proggeramlug commentedon Sep 21, 2026
Closing this report because its specific derived-constructor failure no longer reproduces on current
main; the reason for the difference from the original run is unknown. The newly observed node-fetch failure is tracked independently in #10887.proggeramlug commentedon Sep 21, 2026
Reopening after a fully coherent rebuild of current
main(f88acdaa1b) reproduced the originalMust call super constructorfailure with the clean public-entrynode-fetch@3.3.2fixture. The earlier non-reproduction used a compiler/runtime build containing the pending #10886 changes, so it was not a valid pristine-main result. #10887 remains the next observed blocker on top of that pending fix.proggeramlug commentedon Sep 22, 2026
Confirmed reproducing cleanly on current
mainwhile re-validating node-fetch after its original blocker (#10759) landed. Full fixture:node-fetch@3.3.2,perry.compilePackages: ["node-fetch"], a self-hostedhttp.createServer+fetch()round trip (GET/json, POST/echo). Compiles and links (needs the fullauto-optimizepath — see #10671 for a separate, unrelated link-coherence gap this package also hits underPERRY_NO_AUTO_OPTIMIZE=1), then:Node runs the identical fixture cleanly (
GET json: {"hello":"world"},POST echo: {"a":1}). This is the last blocker standing between node-fetch and a full real-source pass — once this lands, re-validating with the same fixture should confirm the package end-to-end.fix(class): a derived constructor may return an object after super() …
proggeramlug commentedon Oct 4, 2026
Re-checked on main b73093e: the reported "Must call super constructor" no longer reproduces. node-fetch's real Headers.js runs, and so do the URLSearchParams-subclass, builtin-parent, derived-of-derived and async-constructor shapes. A related crash in the same code (a derived constructor returning
new Proxy(this)segfaulted once enough Proxies existed) is fixed by #11933. The node-fetch GET fixture now stops at a separate empty Error, tracked as #10887. Closing this as fixed on main.