Service workers: how offline reading can work
A cleaner opens a staff guide in a building with no reception. The browser needs a saved copy of the guide before that moment. A service worker is one way a web app can arrange that copy and answer requests from it.
Think of it as a request handler
A service worker is a script that can handle requests for pages and files within its scope. It can return cached responses when the network is unavailable. It runs separately from the page.
It does not magically save every file, preserve form entries, or run forever in the background. The builder must define the behavior. Customer records need their own storage and recovery plan.
The first visit still matters
The browser must fetch the service worker and the required files while connected. Registration alone does not prove the cache finished downloading. An interrupted download should not produce a false “ready” message.
For a small reference site, saving the whole guide set can be practical. For a large collection, let readers select downloads and show which ones are complete.
For builders: keep the boundary clear
Use HTTPS for deployment. Supported local-development origins such as localhost allow development testing; opening an HTML file directly is not a service-worker test.
Cache only what the app needs and owns. Do not indiscriminately cache private responses or third-party content. Give each release a distinct cache and define a fallback for uncached navigation.
Treat updates as part of the feature
A new worker can wait while an old one controls open pages. That protects a reading or editing session from an unexpected version change. Plan how the user learns that new content is ready.
Test a real sequence: load version one, disconnect and read, reconnect for version two, then confirm the new release appears without erasing saved work. An offline feature is incomplete until its update behavior has been checked.
Sources & verification
Documentation checked October 25, 2026. Platform instructions are documented guidance; physical-device behavior has not been verified for this article.
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