Remove note about a fetch handler being required alongside DOs - #5185
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Because we're removing that requirement on script upload. It's still often a good idea to bundle a fetch handler with a DO class, but will no longer be required.
koeninger
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Jul 18, 2022
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taylorlee
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Sep 5, 2026
Fixes #15309. The legacy heuristic of assuming anything without a default export is going more harm than good. It also seems like it must have regressed at some point, because it used to be possible to have DO-class-only Workers a [few years ago](cloudflare/cloudflare-docs#5185), even though trying that now would fail by detecting SW syntax. After looking at a bunch of options and various forms of required back-compat, I think the best path forward is to resolve the ambigious case in favor of modules workers. Current heuristic: * default export -> module worker * otherwise -> service worker New heuristic: * no exports -> service worker * default export -> module worker * ambigious exports: - recognized global addEventListener reference -> service worker - otherwise -> module worker This does that the most tricky dynamic constructions of SW can be falsely interpreted as module workers if they have some named exports. I think that's acceptable for a 2 reasons: 1. it is less harmful than misclassifying MW as SW 2. many of the most dynamic constructions (of either MW or SW) can't actually be deployed in practice (due to preexisting validator limitations), so the real breakage is minimal. Alternatives considered: export-only heuristics, source regexes, entrypoint-specific AST matching, an additional parser, and full dependency bundling. These were avoided due to compatibility risks, false positives, added complexity, or resolution overhead.
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Because we're removing that requirement on script upload. It's still
often a good idea to bundle a fetch handler with a DO class, but will no
longer be required.