@runopencode/stencil-signal

Lit (Google's web component framework) started experimental support for signals from @preact\signal-core library. As they stated in their blog:

...we think signals promise to offer a convenient and relatively simple option for shared observable state, a recurring need in our community. So we are starting to explore what it would look like to integrate signals with Lit with a new @lit-labs/preact-signals package.

So, if Lit has it, why Stencil shouldn't?

So this library brings exactly that - integration with @preact\signal-core library which allows you to use signals in your Stencil components. Only requirement is to decorate render() method of your component with @Preactive() decorator and for each value change of signal/computed value used in your render() method, DOM will be updated.

Why? Because we can! Do you need it? Well, probably not, Stencil already has a decent reactivity system. What we believe that Stencil is missing in terms of reactivity is better integration with RxJS library. However, we have compiled some of our commonly used functions in experimental library @runopencode/rx-stencil which you can use to tackle more advanced tasks.

Example

1import { Component, ComponentInterface, h } from '@stencil/core';
2import { Preactive }                        from '@runopencode/stencil-signal';
3import { Signal, signal}                    from '@preact/signals-core';
4
5let counter: Signal<number> = signal<number>('counter', 0);
6
7@Component({
8    tag: 'my-component',
9    shadow: true
10})
11export class MyComponent implements ComponentInterface {
12
13    @Preactive()
14    render(): any {
15        return <div onClick={(): void => { counter.value++; }}>{counter.value}</div>;
16    }
17}

Caveats

In order to avoid memory leaks, and considering that method render() of each component is registered as "effect", cleanup is required which is executed when component is disconnected from DOM. However, Stencil is not consistent in invoking disconnectedCallback() method of components - if your library doesn't have any component which defines this method, Stencil will not invoke it for any component. So, in order to avoid this, you should define this method in at least one component.

For this inconvenience, we intend to open RFC which would address this issue.

TODO:

• Write tests.