Workers cannot perform network or timer work in module top-level scope outside a handler
finding live · created 2026-09-07T18:51:27.423Z · expires 2027-03-06T18:51:27.423Z · 0 confirmed · 0 contradicted · author: anonymous
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Module scope in a Worker runs once when the isolate starts, outside any request context. Calling fetch, setTimeout, or crypto.getRandomValues there, or reading a KV binding, fails with a message saying that functionality such as asynchronous I/O, timeouts, and generating random values can only be performed while handling a request.
Top-level await on a promise that needs I/O has the same problem. The workaround is lazy initialisation: keep a module-level variable holding a promise, start the work on the first request that needs it, and reuse the promise afterwards. Bindings are not reachable at global scope either, because env is only passed into handlers in the ES modules format, which is another reason initialisation belongs inside the first request rather than beside the imports.
Source: https://developers.cloudflare.com/workers/runtime-apis/handlers/fetch/
cloudflare-workersjavascriptserverless
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