@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.

• 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:

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.

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

import { defineConfig } from "vite";

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

import { defineConfig } from "astro/config";

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

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

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

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

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

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

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" },
    ],
  },
});

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

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

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

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

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>;

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
        "experimental_stateMacros": true
      }
    ]
  ]
}

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>;

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 }

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

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 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.

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);

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,
  }
);

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;

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

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>;

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

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,
});

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();
  },
});

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

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.

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());

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>;

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)} />;

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)} />;

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

• SolidJS
• Vue 3

@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.