@preact-signals/utils

@preact-signals/utils is a standard library for Preact Signals, designed to provide essential utilities for comfortable and streamlined usage. This package includes several features to enhance the flexibility and maintainability of Preact Signal-based projects.

Split your code because of you want, not because of you have to

Documentation

Table of Contents

• Prerequisites
  • @preact/signals-core additional step:
  • @preact-signals/safe-react additional step:
  • @preact-signals additional step:
• Installation
• @preact-signals/utils/macro: Macros. Improving ergonomics
  • State macros
  • Ref macro shorthand
  • Macro setup
• Main Entry: @preact-signals/utils
  • ReactiveRef/$
  • WritableReactiveRef/$w
  • ReducerSignal
  • Deep Reactivity (Port of Vue 3 deep tracking API)
    • deepSignal
    • Store API
  • reaction
  • rafReaction
  • accessor/setter
  • resource
  • createFlatStore
  • createFlatStoreOfSignals
• @preact-signals/utils/hooks: Hooks for Signals
  • Deep Reactivity Hooks
  • useLinkedSignal
• @preact-signals/utils/components: Reactive Components
• @preact-signals/utils/hocs: High Order Components (HOCs)
  • reactifyLite
  • Troubleshooting
    • Third party libraries is not working with HOCs
  • Setup
• Inspired by:

Prerequisites

Ensure that one of the preact signals runtimes is installed:

• @preact/signals for preact, requiring an additional step.
• @preact/signals-core for vanilla js requiring an additional step.
• @preact-signals/safe-react for react, requiring an additional step.
• @preact/signals-react for react.

@preact/signals-core additional step:

We need to resolve @preact/signals-react as @preact/signals-core

Vite example:

import { defineConfig } from "vite";

export default defineConfig({
  resolve: {
    alias: {
      "@preact/signals-react": "@preact/signals-core",
    },
  },
});

Astro example:

import { defineConfig } from "astro/config";

// https://astro.build/config
export default defineConfig({
  vite: {
    resolve: {
      alias: {
        "@preact/signals-react": "@preact/signals-core",
      },
    },
  },
});

@preact-signals/safe-react additional step:

Resolve @preact-signals/safe-react as @preact/signals-react

Vite example:

// vite.config.ts
import { defineConfig } from "vite";

export default defineConfig({
  resolve: {
    alias: {
      "@preact/signals-react": "@preact-signals/safe-react",
    },
  },
});

Astro example:

// astro.config.mjs
import { defineConfig } from "astro/config";

// https://astro.build/config
export default defineConfig({
  vite: {
    resolve: {
      alias: {
        "@preact/signals-react": "@preact/signals-core",
      },
    },
  },
});

Next.js

// next.config.js
module.exports = {
  webpack: (config) => {
    config.resolve.alias = {
      ...config.resolve.alias,
      "@preact/signals-react": "@preact-signals/safe-react",
    };
    return config;
  },
};

@preact/signals additional step:

Resolve @preact/signals-react as @preact/signals. For guidance, see resolve react as preact and follow a similar process with signals. Additionally, dedupe preact.

Vite example:

import preact from "@preact/preset-vite";
import { defineConfig } from "vite";

export default defineConfig({
  plugins: [preact()],
  resolve: {
    dedupe: ["preact"],
    alias: [
      { find: "react", replacement: "preact/compat" },
      { find: "react-dom/test-utils", replacement: "preact/test-utils" },
      { find: "react-dom", replacement: "preact/compat" },
      { find: "react/jsx-runtime", replacement: "preact/jsx-runtime" },
      { find: "@preact/signals-react", replacement: "@preact/signals" },
    ],
  },
});

Installation

Fetch @preact-signals/utils via your preferred package manager:

# Using npm
npm install @preact-signals/utils

# Using yarn
yarn add @preact-signals/utils

# Using pnpm
pnpm add @preact-signals/utils

Library consist from many entries:

• @preact-signals/utils library agnostic utils and deep reactivity implementation
• @preact-signals/utils/components for reactive components
• @preact-signals/utils/hooks for reactive hooks
• @preact-signals/utils/hocs provides hocs wrappers that bring reactivity to your components
• @preact-signals/utils/macro provides babel macros

@preact-signals/utils/macro: Macros. Improving ergonomics

This entry provides macros distributed as babel plugin. It's allows you to write more concise code. There are two types of macros: state macros, and ref macro shorthand. You can play with it in the interactive playground

State macros

Shorthands that allows you to do omit .value access and work with signals like with regular values. Allowed state macros:

• $state
• $useState
• $useLinkedState
• $derived
• $useDerived
• $deref

Here is example of how it works. You can play with it here

Ref macro shorthand

import { $$ } from "@preact-signals/utils/macro";

const a = signal(1);
const b = signal(2);

// $$ is macro, which will be replaced with $(() => ...)
// $$(a.value + b.value) -> $(() => a.value + b.value)
// C component will not be reexecuted if a or b changed
const C = () => <div>{$$(a.value + b.value)}</div>;

Macro setup

To use macros you need to add babel plugin to your babel config:

// babel.config.json
{
  "plugins": [
    [
      "module:@preact-signals/utils/babel",
      {
        // if you want to use stateMacros
        "stateMacros": true
      }
    ]
  ]
}

Main Entry: @preact-signals/utils

ReactiveRef/$

The ReactiveRef type functions similarly to a Preact signal, essentially wrapping a function that can be passed into props or JSX. You can create it using the $ function.

const sig = signal(1);
<div>{$(() => sig.value * 10)}</div>;

WritableReactiveRef/$w

Creates editable signal from getter and setter functions.

const a = signal({ a: 1 });
const aField = $w({
  get() {
    return a.value.a;
  },
  set(value) {
    a.value = { a: value };
  },
});

console.log(aField.value); // 1
aField.value = 2;
console.log(aField.value); // 2
console.log(a.value); // { a: 2 }

ReducerSignal

Reducer pattern for signals

const reducer = (it: number, action: { type: "increment" | "decrement" }) => {
  switch (action.type) {
    case "increment":
      return it + 1;
    case "decrement":
      return it - 1;
  }
};
const counter = reducerSignal(0, reducer);
effect(() => {
  console.log("counter value", counter.value);
});
// prints 1
counter.dispatch({ type: "increment" });
// dispatch can be destructured, other parameters not
const { dispatch } = reducerSignal;
// prints 2
dispatch({ type: "increment" });

Implementation

Deep Reactivity (Port of Vue 3 deep tracking API)

deepSignal

Takes an inner value and returns a reactive and mutable signal, with deepReactive inside of it.

const a = deepSignal({ a: 1, b: 2 });
const c = computed(() => a.value.a + a.value.b);
a.value = { a: 2, b: 3 };
console.log(c.value); // 5

a.value.b = 4;
console.log(c.value); // 6

Store API

Store API contains Vue-like API for deep reactivity. It's has one significant change: if reactive wrapper is deep - it will be named with deep prefix. So reacitve becomes deepReactive.

Vue	@preact-signals/utils/store
reactive	Store.deepReactive
readonly	Store.deepReadonly
shallowReadonly	Store.shallowReadonly
shallowReactive	Store.shallowReactive
isReactive	Store.isReactive
isReadonly	Store.isReadonly
isProxy	Store.isProxy
toRaw	Store.toRaw
markRaw	Store.markRaw

To use Store API you should wrap your object with Store.deepReactive or Store.shallowReactive:

import { Store } from "@preact-signals/utils";

const a = Store.deepReactive({ a: 1, b: 2 });
const b = Store.shallowReactive({ a: 1, b: 2 });

const c = computed(() => a.value.a + a.value.b + b.value.a + b.value.b);

reaction

The reaction function allows responding to changes tracked within a dependent function. It is useful for managing side-effects or synchronizing non-reactive parts of your code.

reaction is enhanced version of this:

const reaction = (deps, fn) =>
  effect(() => {
    const value = deps();
    untracked(() => fn(value));
  });

const sig = signal(1);
const sig2 = signal(2);
// reaction(deps, effect, options?: {memoize: boolean})
const dispose = reaction(
  () => sig.value,
  (value) => {
    // you can read signals here without tracking
    if (sig2.value * 10 === value) {
      sig2.value = value;
    }
  }
);

// will only reexecute reaction if deps result actually changed
reaction(
  () => {
    sig.value;
    return sig2.value;
  },
  () => {
    console.log("reacted");

    return () => {
      console.log("reaction disposed");
    };
  },
  {
    memoize: true,
  }
);

rafReaction

Will execute reaction after deps changed on next animation frame. Return dispose function.

const sig = signal(1);
const el = document.createElement("div");

rafReaction(
  // deps
  () => sig.value,
  // effect
  (value) => {
    el.style.transform = `translateX(${value}px)`;
  }
);

sig.value = 10;

accessor/setter

These functions act as wrapper creators for signals, offering a convenient way to separate reading and writing responsibilities.

resource

The resource type binds a signal to a promise, including Preact Signals' reactivity. It can be retried, rejected, or resolved, offering a streamlined way to manage asynchronous operations.

const [resource, { refetch }] = createResource({
  fetcher: async () => {
    const response = await fetch("https://example.com");
    return response.json();
  },
});

return <Show when={resource}>{(result) => <div>{result()}</div>}</Show>;

createFlatStore

This function offers a simple store implementation, converting key values into signals on demand.

When deep reactivity API will be stable, possibly flat stores will be deprecated

const [store, setStore] = createFlatStore({
  a: 1,
  b: 2,
  // computeds will be created from getters
  get c() {
    return this.a + this.b;
  },
});

const c = computed(() => store.a + store.b); // 3
store.a = 2;
store.b = 3;
console.log(store.c); // 5
console.log(c.value); // 5

// will be auto bached
setStore({ a: 3, b: 4 });
console.log(c.value); // 7

createFlatStoreOfSignals

This function wraps provided signals and value to flat store. You can pass computed's too and it will be readonly field

When deep reactivity API will be stable, possibly flat stores will be deprecated

const [store, setStore] = createFlatStoreOfSignals({
  a: 1,
  b: 2,
  c: signal(10),
  d: computed(() => 10),
  // computeds will be created from getters
  get e() {
    return this.a + this.b;
  },
});

// ok
setStore({
  a: 10,
  b: 11,
  c: 12,
});

setStore({
  // type error and throws
  e: 10,
  d: 10,
});

@preact-signals/utils/hooks: Hooks for Signals

This entry provides hooks designed to work with signals, enhancing reactivity and composability in your components.

It provides hooks like

• useSignalEffectOnce

• useComputedOnce

• useInitSignal

• useReducerSignal

• useReaction

• useLinkedSignal

• useResource

• useFlatStore

• useFlatStoreOfSignals

• useComputedFlatStore

• useDeepSignal

• useDeepReactive

• useShallowReactive

// execute function run only once, and you can access other signals inside without tracking
const a = useInitSignal(() => new Set());
// uses first provided clojure, so it can be jit
const b = useComputedOnce(() => a.value.size);
useSignalEffectOnce(() => a.value.size);

// create flat store from provided value
const [store, setStore] = useFlatStore(() => ({
  a: 1,
  b: 2,
}));

const [store2, setStore2] = useFlatStoreOfSignals(() => ({
  a: 1,
  b: signal(10),
}));

// create resource from provided fetcher
const [resource, { refetch }] = useResource({
  fetcher: async () => {
    const response = await fetch("https://example.com");
    return response.json();
  },
});

Deep Reactivity Hooks

Exports hook which takes as first argument callback which will be applied on the first rended to create reactive primitive.

useDeepSignal

Takes creator callback and returns a reactive and mutable signal, with deepReactive inside of it.

const a = useDeepSignal(() => ({ a: 1, b: 2 }));

There are also: useDeepReactive, useShallowReactive.

useLinkedSignal

Creates signal that linked to value passed to hook, with unwrapping of signals to avoid .value.value

// always linked to value passed to hook
const s1 = useLinkedSignal(Math.random() > 0.5 ? 1 : 0);
// 0 | 1
console.log(s1.peek());

const s2 = useLinkedSignal(Math.random() > 0.5 ? signal(true) : false);
// false | true
console.log(s2.peek());

// deeply unwrapping
const s3 = useLinkedSignal(signal(signal(signal(false))));
// false
console.log(s3.peek());

@preact-signals/utils/components: Reactive Components

This section includes components like Show, Switch, Match, For, allowing you to scope reactivity within your JSX. These components aid in writing more declarative and readable code. All of this component works with reactive unit, which is Signal or Accessor callback

import { Show, For } from "@preact-signals/utils/components";

<Show fallback={<p>Loading...</p>} when={() => arr.value}>
  {(data) => (
    <ul>
      <For each={data} keyExtractor={(item) => item.id}>
        {(item) => <li>{renderItem(item)}</li>}
      </For>
    </ul>
  )}
</Show>;

import { Switch, Match } from "@preact-signals/utils/components";

<Switch fallback={<p>Not found</p>}>
  <Match when={() => route.value === "home"}>
    <Home />
  </Match>
  <Match when={() => route.value === "about"}>
    <About />
  </Match>
  <Match when={() => route.value === "users"}>
    <Users />
  </Match>
</Switch>;

@preact-signals/utils/hocs: High Order Components (HOCs)

HOCs in this entry allow you to inject signals or ReactiveRef-s into props, aiding in the creation of reusable and composable logic across various components.

Examples:

const View$ = withSignalProps(View);
const Text$ = withSignalProps(Text);
const a = signal(10);
const b = signal(5);

<View$ hitSlop={useComputed(() => a.value + b.value)} />;
<View$ hitSlop={$(() => a.value + b.value)} />;

reactifyLite

Makes you component truly reactive. Your props are will be use getter to signals under the hood (destructuring forces a whole component to rerender - so you should avoid it). So you can safely pass it into effect or reactive component like Show or Switch without worries about tracking.

const Comp = (props: ReactiveProps<{ a: number }>) => (
  <Show when={() => props.a > 10}>{(v) => v + 10}</Show>
);

const B = reactifyLite(Comp);
<B a={$(() => a.value + b.value)} />;

Troubleshooting

Third party libraries is not working with HOCs while using @preact-signals/safe-react or @preact/signals-react with babel

If you are using reactifyLite or withSignalProps and you component has no reaction on signal changes, probably parent the component has no signals tracking.

• @preact-signals/safe-react solution is to wrap component with HOC withTrackSignals to ensure that all signals will be tracked.

import { withTrackSignals } from "@preact-signals/safe-react/manual";
import { withSignalProps } from "@preact-signals/utils/hocs";

const View$ = withSignalProps(withTrackSignals(View));

• @preact/signals-react has no withTrackSignals HOC, but we can use this workaround:

import { useSignals } from "@preact/signals-react/runtime";

/**
 * @useSignals
 */
const _View = (...args) => View(...args);

const View$ = withSignalProps(_View);

If you wrapped some component with

Heavily inspired by:

• SolidJS
• Vue 3

License

@preact-signals/utils is licensed under the MIT License, and you're free to use, modify, and distribute it under the terms outlined in the LICENSE file.