comlink-ipc

Fork

Forked from GoogleChromeLabs/comlink to remove dependency on browser webworkers and MessageChannel and use more generically indepdent of transport.

API

Comlink.wrap(endpoint) and Comlink.expose(value, endpoint?)

Comlink’s goal is to make exposed values from one thread available in the other. expose exposes value on endpoint, where endpoint is a [postMessage-like interface][endpoint].

wrap wraps the other end of the message channel and returns a proxy. The proxy will have all properties and functions of the exposed value, but access and invocations are inherently asynchronous. This means that a function that returns a number will now return a promise for a number. As a rule of thumb: If you are using the proxy, put await in front of it. Exceptions will be caught and re-thrown on the other side.

Lastly, you can use Comlink.proxy(value). When using this Comlink will not copy the value, but instead send a proxy. Both threads now work on the same value. This is useful for callbacks, for example, as functions are not structured cloneable.

myProxy.onready = Comlink.proxy(data => {
  /* ... */
});

Transfer handlers and event listeners

It is common that you want to use Comlink to add an event listener, where the event source is on another thread:

button.addEventListener("click", myProxy.onClick.bind(myProxy));

While this won’t throw immediately, onClick will never actually be called. This is because [Event][event] is neither structured cloneable nor transferable. As a workaround, Comlink offers transfer handlers.

Each function parameter and return value is given to all registered transfer handlers. If one of the event handler signals that it can process the value by returning true from canHandle(), it is now responsible for serializing the value to structured cloneable data and for deserializing the value. A transfer handler has be set up on both sides of the message channel. Here’s an example transfer handler for events:

Comlink.transferHandlers.set("EVENT", {
  canHandle: obj => obj instanceof Event,
  serialize: ev => {
    return [{
      target: {
        id: ev.target.id
        classList: [...ev.target.classList]
      }
    }, []];
  },
  deserialize: obj => obj,
});

Note that this particular transfer handler won’t create an actual Event, but just an object that has the event.target.id and event.target.classList property. Often, this enough. If not, the transfer handler can be easily augmented to provide all necessary data.

License Apache-2.0