sw

The assembly

install(options) wires fetch, message, and activate listeners on the worker scope and returns {cacheTier, coalescer, bundle, hub}. The deployable worker is a few lines:

// sw.js — bundle this, then register the output with {type: 'module'}
import {install} from 'double-meh-sw/sw.js';

install({
  version: '2026.07.04',
  match: '/api/',
  cache: {cacheName: 'app-shared'},
  bundler: {url: '/bundle', match: '/api/'}
});

A module service worker does not resolve bare specifiers: serving this file unbundled fails registration outright. Ship the bundled output, or import by URL — /node_modules/double-meh-sw/src/sw.js.

Options

Option	Default	Meaning
scope	globalThis	The worker scope — injectable, which is how the whole suite runs on Node/Bun/Deno.
version	—	Reported over io:version and in the io:hello reply.
match	same-origin, non-navigation	Which GETs the worker handles at all: a URL prefix, RegExp, or predicate.
cache	{cacheName: 'io-shared'}	Cache tier options.
bundler	off	Bundle window options plus its own match for eligibility.
fetch	globalThis.fetch	The upstream — injectable for tests and mocks.
claim	true	clients.claim() on activate.

Serve order

Cache tier hit → bundle window (configured, matched, and the client did not announce a library — client-wins) → coalesced network. Non-GETs and unmatched requests are never touched.

Two rules shape everything:

• The respondWith decision is synchronous — only the matcher gates it; all async work happens after.
• Everything degrades to plain fetches — bundler trouble, missing parts, lone-request windows: the worker must be a no-op-degradable adornment. If it vanishes entirely (first visit, hard reload), the app is logically unchanged. The cache tier is held to the same rule: a read or write that throws — a quota error is the ordinary case — is a miss and a no-op, never a failed request. Only the network may fail a request.

See also: Messages, Cache tier.