A better way of working with web workers
A better way of working with web workers. Uses JavaScript Proxies to make communcation with web workers similar to interacting with normal objects.
Web workers are great to offload work to a different thread in browsers. However, the messaging based API is not very easy to work with. This library makes working with web workers similar to how you'd interact with a local object, thanks to the power of proxies.
npm install web-worker-proxy
or
yarn add web-worker-proxy
First, we need to wrap our worker:
// app.js import { create } from 'web-worker-proxy';const worker = create(new Worker('worker.js'));
Inside the web worker, we need to wrap the target object to proxy it:
// worker.js import { proxy } from 'web-worker-proxy';proxy({ name: { first: 'John', last: 'Doe' }, add: (a, b) => a + b, });
Now we can access properties, call methods etc. by using the
awaitkeyword, or passing a callback to
then:
console.log(await worker.name.first); // 'John'// or
worker.name.first.then(result => { console.log(result); // 'John' });
Accessing properties is lazy, so the actual operation doesn't start until you await the value or call
thenon it.
You can access any serializable properties on the proxied object asynchronously:
// Serializable values console.log(await worker.name);// Nested properties console.log(await worker.name.first);
// Even array indices console.log(await worker.items[0]);
When accessing a property, you'll get a thenable (an object with a
thenmethod), not an normal promise. If you want to use it as a normal promise, wrap it in
Promise.resolve:
// Now you can call `catch` on the promise Promise.resolve(worker.name.first).catch(error => { console.log(error); });
You can add a new property on the proxied object, or create a new one. It can be a nested property too:
worker.thisisawesome = {}; worker.thisisawesome.stuff = 42;
You can call methods on the proxied object, and pass any serializable arguments to it. The method will return a promise which will resolve to the value returned in the worker. You can also catch errors thrown from it:
try { const result = await worker.add(2, 3); } catch (e) { console.log(e); }
The method on the proxied object can return any serializable value or a promise which returns a serializable value.
It's also possible to pass callbacks to methods, with some limitations:
worker.methods.validate(result => { console.log(result); });
To prevent memory leaks, callbacks are cleaned up as soon as they are called. Which means, if your callback is supposed to be called multiple times, it won't work. However, you can persist a callback function for as long as you want with the
persisthelper. Persisting a function keeps around the event listeners. You must call
disposeonce the function is no longer needed so that they can be cleaned up.
import { persist } from 'web-worker-proxy';const callback = persist(result => { if (result.done) { callback.dispose(); } else { console.log(result); } });
worker.subscribe(callback);
create(worker: Worker)
Create a proxy object which wraps the worker and allows you to interact with the proxied object inside the worker. It can take any object which implements the
postMessageinterface and the event interface (
addEventListenerand
removeListener).
proxy(object: Object, target?: Worker = self)
Proxy an object so it can be interacted with. The first argument is the object to proxy, and the second argument is an object which implements the
postMessageinterface and the event interface, it defaults to
self. It returns an object with a
disposemethod to dispose the proxy.
There can be only one proxy active for a given target at a time. To proxy a different object, we first need to dispose the previous proxy first by using the
disposedmethod.
persist(function: Function)
Wrap a function so it can be persisted when passed as a callback. Returns an object with a
disposemethod to dispose the persisted function.
The library expects the
Proxyand
WeakMapconstructors to be available globally. If you are using a browser which doesn't support these features, make sure to load appropriate polyfills.
The following environments support these features natively: Google Chrome >= 49, Microsoft Edge >= 12, Mozilla Firefox >= 18, Opera >= 36, Safari >= 10, Node >= 6.0.0.
The library leverages proxies to intercept actions such as property access, function call etc., and then the details of the actions are sent to the web worker via the messaging API. The proxied object in the web worker recieves and performs the action, then sends the results back via the messaging API. Every action contains a unique id to distinguish itself from other actions.
While developing, you can run the example app and open the console to see your changes:
yarn example
Make sure your code passes the unit tests, Flow and ESLint. Run the following to verify:
yarn test yarn flow yarn lint
To fix formatting errors, run the following:
yarn lint -- --fix