Workers

Dedicated workers dedicated-workers

Baseline: Widely available on the web, in every major browser since Jul 2015, and long enough to count on (since Jan 2018).

niso: Partial 85%. 410 of 477 subtests pass, by system: Linux 85%, macOS 85%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · DedicatedWorkerGlobalScope, Worker, WorkerGlobalScope, WorkerLocation

Channel messaging channel-messaging

Baseline: Widely available on the web, in every major browser since Sep 2015, and long enough to count on (since Mar 2018).

niso: Partial 88%. 340 of 385 subtests pass, by system: Linux 88%, macOS 88%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · MessageChannel, MessageEvent, MessagePort

BroadcastChannel broadcast-channel

Baseline: Widely available on the web, in every major browser since Mar 2022, and long enough to count on (since Sep 2024).

niso: Partial 61%. 47 of 76 subtests pass, by system: Linux 61%, macOS 61%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · BroadcastChannel

new Worker(url) works as on the web: a dedicated worker runs its script on a thread of its own, with a DedicatedWorkerGlobalScope, and talks to the page with postMessage. Messages are structured clones, and MessageChannel and BroadcastChannel exist. A worker’s script and its importScripts load through the page’s own loader, so a worker’s script can come from the app’s bundle like the page’s. It must be same-origin or a data: URL.

Shared workers and service workers aren’t implemented. With no service worker there’s no offline cache or push from a worker; a niso app’s files are local anyway.

How it runs

Each worker gets a DOM of its own (without a document) and an engine of its own on its thread, and runs its own event loop. Nothing in the page’s DOM is shared with it; only messages cross. Workers need a worker host: niso-core’s WorkerHost trait (crates/niso-core/src/worker.rs), whose C forms are a runner that starts the thread itself (niso_dom_set_worker_runner) or a host that starts workers on threads of its own (niso_dom_set_worker_host). The JS binding on QuickJS sets a runner, so a page’s workers run on QuickJS like the page; Node-API sets a host that runs each worker on one of the runtime’s worker threads. Porffor runs no workers: with no worker host, new Worker() throws a NotSupportedError.

While a worker is busy, the page’s event loop runs in real time rather than skipping ahead on virtual time, so tests that use workers take as long as the workers do. Freeing a page ends its workers, waiting up to two seconds.

The C side is Workers.