fix(cloudflare): Honor newTarget in instrumentDurableObjectWithSentry construct trap#22104
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andreiborza merged 1 commit intoJul 8, 2026
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… construct trap The construct trap created instances with `new target(...)`, ignoring newTarget. Subclasses of the instrumented class - such as miniflare's local-explorer wrapper, which extends every user Durable Object class to add introspection methods - lost their own prototype: subclass methods disappeared and instanceof checks against the subclass failed. Construct through Reflect.construct with newTarget so the subclass prototype is preserved. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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hi @martijnwalraven, thanks for fixing this, looks good!
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This PR adds the external contributor to the CHANGELOG.md file, so that they are credited for their contribution. See #22104 Co-authored-by: andreiborza <168741329+andreiborza@users.noreply.github.com>
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instrumentDurableObjectWithSentryreturns aProxywhoseconstructtrap creates the instance withnew target(context, instrumentedEnv), ignoring the trap'snewTargetargument.When a subclass of the instrumented class is constructed, the instance therefore gets the base class's prototype instead of the subclass's: subclass prototype methods disappear and
instanceof Subclassis false. This breaks tooling that subclasses the exported (instrumented) Durable Object class — for example miniflare's local-explorer wrapper (do-wrapper.worker.tswraps every user Durable Object class inclass Wrapper extends UserClasswith introspection methods on the wrapper prototype), whose methods become unreachable when the wrapped class is Sentry-instrumented.Fix: construct through
Reflect.construct(target, [context, instrumentedEnv], newTarget)so the subclass prototype is preserved. The instrumented Durable Object methods (fetch,alarm,webSocket*) are assigned as own properties on the instance, so instrumentation behavior is unchanged; the existing "preserves constructor identity on the proxy" test still passes.Added a regression test that subclasses the instrumented class and asserts the subclass method is callable,
instanceofholds, and the built-in handlers remain instrumented.🤖 Generated with Claude Code