comlink
Comlink makes WebWorkers enjoyable.
Tiny JavaScript library from Google Chrome Labs that makes web worker background threads as easy as calling regular functions, hiding complex message-passing behind simple async/await syntax.
Web browsers run JavaScript on a single thread by default, which means every calculation, animation, and user interaction competes for the same execution slot. When a page does something computationally heavy, like processing a large file or running complex calculations, the interface can freeze or become unresponsive because that single thread is busy. Web Workers are a browser feature that lets you run JavaScript code in a separate background thread, keeping the main thread free for user interactions. The problem is that communicating between threads requires a message-passing API called postMessage, which is low-level and awkward to work with.
Comlink is a small library from Google Chrome Labs that hides that complexity. Instead of manually sending and receiving messages, you write code that calls functions on a worker almost as if they were regular local functions. Comlink translates those calls into the underlying message-passing automatically. Because the communication is still asynchronous (one thread cannot directly read the other's memory), your function calls return promises, which you wait for using the standard async/await syntax in JavaScript.
The practical result is that moving expensive work off the main thread becomes much less code and much less mental overhead. The library is tiny at about 1.1 kilobytes compressed, so adding it to a web page has virtually no size impact.
Comlink also handles passing callbacks between threads, transferring large binary data efficiently without copying it (using the browser's built-in transfer mechanism), and working with shared workers (a variant of web workers that multiple browser tabs can connect to simultaneously).
The library is maintained under the GoogleChromeLabs organization on GitHub, which publishes tools and experiments from the Chrome team. It works in all modern browsers including Chrome, Firefox, Safari, and Edge. The README includes working code examples and documents the full API. No server-side component is needed; this is entirely a browser-side tool for improving the performance and responsiveness of client-facing web applications.
Where it fits
- Move expensive calculations off the browser's main thread to keep the user interface responsive during heavy processing.
- Run file parsing or data transformation in a background worker without writing complex postMessage boilerplate.
- Share a single background worker thread across multiple open browser tabs using a shared worker.
- Transfer large binary data such as images or audio buffers between threads without copying them, using the browser's transfer mechanism.