Worker Isolation

By default, all jiki operations run on the main thread. The worker option offloads CPU-intensive transpilation (TypeScript, JSX, TSX) to a Web Worker via esbuild-wasm, preventing UI freezes during compilation.

Quick start

import { boot } from "@run0/jiki";

const container = boot({ worker: true });
await container.init(); // esbuild transpiler runs in a Web Worker

Worker modes

Mode	Behaviour
`false`	Everything on the main thread (default)
`true`	Transpilation runs in a Web Worker
`'auto'`	Use workers when `Worker` is available (browser), skip in Node.js

What gets offloaded

Currently, worker mode offloads esbuild-wasm transpilation: converting TypeScript, JSX, and TSX to JavaScript. This is the single most expensive operation and the primary cause of UI freezes during development.

Module resolution, code execution, and VFS operations continue to run on the main thread. Full kernel isolation (moving require() and code execution to a worker) is planned for a future release.

When to use

For interactive playgrounds, enable worker: true or 'auto' to keep the UI responsive while users edit TypeScript files.
If you’re installing packages and running code in sequence without a UI, false (the default) is fine.
Workers are not needed in Node.js environments.

Browser requirements

Worker mode uses esbuild’s built-in Web Worker support. No special headers (COOP/COEP) are required for this level of isolation.