fix(client): stop native fetch from throwing Illegal invocation in browsers

[dinwwwh]

Passing the browser's native fetch straight to a link, such as fetch: globalThis.fetch or fetch: window.fetch, no longer fails every request with TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation. The transport now calls the custom fetch without a receiver, so RPCLink and OpenAPILink both work with native fetch passed directly.

Fixes

• The custom fetch option was called as a method on the transport. Browsers reject native fetch when its this is anything other than the global object. Node's fetch does not check this, so existing tests never caught this.
• Wrapped forms like (url, init) => globalThis.fetch(url, init), which the docs use, already worked and are unaffected.

Testing

• Headless Chrome against a real oRPC server with the client bundled from source: before the fix, the default fetch worked and both globalThis.fetch and window.fetch threw Illegal invocation. After the fix, all three return the response.
• New test asserts the custom fetch is called with this set to undefined. It fails with the old this.fetch(...) call and passes with the fix.
• Client and OpenAPI fetch adapter tests, eslint, and @orpc/client type:check pass.

[pullfrog]

✅ No new issues found.

Reviewed changes

• Receiver-free custom fetch — FetchLinkTransport.send now hoists this.fetch into a local before calling it, so native browser fetch no longer receives the transport instance as this. In strict-mode ES modules the bare call yields this === undefined, which is the accepted form for global fetch; the default (globalThis.fetch)(...) wrapper was already correct.
• Regression test — asserts fetch.mock.contexts equals [undefined]. This genuinely pins the bug: the previous this.fetch(...) invocation records the transport instance as context, so the test fails before the fix and passes after.
• Coverage — @orpc/openapi's OpenAPILink reuses the same FetchLinkTransport, so it inherits the fix; a repo-wide search found no other site that invokes a custom fetch as a method.

  ^{｜ View workflow run ｜ Using DeepSeek Flash (free via Pullfrog for OSS) ｜ 𝕏}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[pkg-pr-new]

More templates

• @orpc/bun-playground
• @orpc/cloudflare-playground
• @orpc/nest-playground
• @orpc/next-playground

@orpc/ai-sdk

npm i https://pkg.pr.new/@orpc/ai-sdk@2112

@orpc/arktype

npm i https://pkg.pr.new/@orpc/arktype@2112

@orpc/bun

npm i https://pkg.pr.new/@orpc/bun@2112

@orpc/client

npm i https://pkg.pr.new/@orpc/client@2112

@orpc/cloudflare

npm i https://pkg.pr.new/@orpc/cloudflare@2112

@orpc/contract

npm i https://pkg.pr.new/@orpc/contract@2112

@orpc/experimental-effect

npm i https://pkg.pr.new/@orpc/experimental-effect@2112

@orpc/evlog

npm i https://pkg.pr.new/@orpc/evlog@2112

@orpc/hibernation

npm i https://pkg.pr.new/@orpc/hibernation@2112

@orpc/json-schema

npm i https://pkg.pr.new/@orpc/json-schema@2112

@orpc/experimental-lock

npm i https://pkg.pr.new/@orpc/experimental-lock@2112

@orpc/experimental-msw

npm i https://pkg.pr.new/@orpc/experimental-msw@2112

@orpc/nest

npm i https://pkg.pr.new/@orpc/nest@2112

@orpc/next

npm i https://pkg.pr.new/@orpc/next@2112

@orpc/node

npm i https://pkg.pr.new/@orpc/node@2112

@orpc/openapi

npm i https://pkg.pr.new/@orpc/openapi@2112

@orpc/opentelemetry

npm i https://pkg.pr.new/@orpc/opentelemetry@2112

@orpc/pinia-colada

npm i https://pkg.pr.new/@orpc/pinia-colada@2112

@orpc/pino

npm i https://pkg.pr.new/@orpc/pino@2112

@orpc/publisher

npm i https://pkg.pr.new/@orpc/publisher@2112

@orpc/ratelimit

npm i https://pkg.pr.new/@orpc/ratelimit@2112

@orpc/server

npm i https://pkg.pr.new/@orpc/server@2112

@orpc/shared

npm i https://pkg.pr.new/@orpc/shared@2112

@orpc/swr

npm i https://pkg.pr.new/@orpc/swr@2112

@orpc/tanstack-query

npm i https://pkg.pr.new/@orpc/tanstack-query@2112

@orpc/trpc

npm i https://pkg.pr.new/@orpc/trpc@2112

@orpc/valibot

npm i https://pkg.pr.new/@orpc/valibot@2112

@orpc/zod

npm i https://pkg.pr.new/@orpc/zod@2112

commit: 7a842c6

[codspeed]

Merging this PR will not alter performance

✅ 30 untouched benchmarks

---

_{Comparing dinwwwh:claude/fetch-illegal-invocation-fix-b1c195 (7a842c6) with main (dfa4e1e)}