📶 @deepsignal/preact

This library is meant to expand on Preact's new Signal primitive to make it a viable state management solution at the scale of a full state management system by wrapping the built in primitive with a new DeepSignal model. This package is intended for use with Preact applications only.

Installation

1# npm
2npm i @deepsignal/preact @preact/signals
3# yarn
4yarn add @deepsignal/preact @preact/signals
5# pnpm
6pnpm add @deepsignal/preact @preact/signals

This package also requires @preact/signals as peer dependencies, as well as preact itself (although the commands above assume you have preact already installed).

Why use @deepsignal/preact?

In a current Preact application you would be easily tempted to use a state management solution from the React ecosystem which relies on the VDOM. If you use a library like this then then your application wide state updates could be causing full VDOM rerenders. Signals provide us an escape from that on the scale of micro-state, but this library aims to scale that solution for larger applications.

How it works

Very simply, the library just takes an arbitrary object of any scale or shape, and recursively turns all properties into signals. The objects themselves each turn into a DeepSignal which contains a value getter & setter as well as a peek method just like regular Signal instances. However, if you assign a new value to a DeepSignal, the setter method will recursively find every true Signal inside the object and assign them to a new value. So if you subscribe to a Signal in a component, you can guarantee that it will be updated no matter what level of the store gets reassigned.

So a simple example like this

1import { deepSignal } from "@deepsignal/preact";
2
3const userStore = deepSignal({
4  name: {
5    first: "Thor",
6    last: "Odinson"
7  },
8  email: "thor@avengers.org"
9});

...is equivalent to this code...

1import { signal, batch } from "@preact/signals";
2
3const userStore = {
4  name: {
5    first: signal("Thor"),
6    last: signal("Odinson"),
7    get value(): { first: string, last: string } {
8      return {
9        first: this.first.value,
10        last: this.last.value
11      }
12    },
13    set value(payload: { first: string, last: string }) {
14      batch(() => {
15        this.first.value = payload.first;
16        this.last.value = payload.last;
17      });
18    },
19    peek(): { first: string, last: string } {
20      return {
21        first: this.first.peek(),
22        last: this.last.peek()
23      }
24    },
25  },
26  email: signal("thor@avengers.org"),
27  get value(): { name: { first: string, last: string }, email: string } {
28    return {
29      name: {
30        first: this.name.first.value,
31        last: this.name.last.value
32      },
33      email: this.email.value
34    }
35  },
36  set value(payload: { name: { first: string, last: string }, email: string }) {
37    batch(() => {
38      this.name.first.value = payload.name.first;
39      this.name.last.value = payload.name.last;
40      this.email.value = payload.email;
41    });
42  },
43  peek(): { name: { first: string, last: string }, email: string } {
44    return {
45      name: {
46        first: this.name.first.peek(),
47        last: this.name.last.peek()
48      },
49      email: this.email.peek()
50    }
51  },
52};

Side note for "How it works"

This example is now somewhat antiquated. Starting with version 4.0.0, part of the DeepSignal model tracks it's own structural shape. This way you can store modifiable records of nested DeepSignals & Signals. The example above is still the most simple representation of the most common use case for DeepSignals. However, it is not a perfect representation of all of it's capabilities.

Using DeepSignal in a local context

By utilizing useDeepSignal you can get a local state DX that's very similar to class components while continuing to have the performance advantages of signals.

1import { useDeepSignal } from "@deepsignal/preact";
2
3const UserRegistrationForm = () => {
4  const user = useDeepSignal(() => ({
5    name: {
6      first: "",
7      last: ""
8    },
9    email: ""
10  }));
11
12  const submitRegistration = (event) => {
13    event.preventDefault();
14    fetch(
15      "/register",
16      { method: "POST", body: JSON.stringify(user.peek()) }
17    );
18  }
19
20  return (
21    <form onSubmit={submitRegistration}>
22      <label>
23        First name
24        <input value={user.name.first}
25          onInput={e => user.name.first.value = e.currentTarget.value} />
26      </label>
27      <label>
28        Last name
29        <input value={user.name.last}
30          onInput={e => user.name.last.value = e.currentTarget.value} />
31      </label>
32      <label>
33        Email
34        <input value={user.email}
35          onInput={e => user.email.value = e.currentTarget.value} />
36      </label>
37      <button>Submit</button>
38    </form>
39  );
40}

TypeScript support

The API for deepStore and useDeepStore will handle dynamic typing for arbitrary input! It will also help you avoid a case like this

1import { deepSignal } from "@deepsignal/preact";
2
3const userStore = deepSignal({
4  name: {
5    first: "Thor",
6    last: "Odinson"
7  },
8  email: "thor@avengers.org"
9});
10
11// TS error: Cannot assign to 'email' because it is a read-only property.
12userStore.value.email = "another@email.com"

Recipes

Zustand style method actions

When I look to Zustand for the API it provides, it seems like a lot of their API (as much as I admire it) is based around supporting the functional context. But the output of @deepsignal/preact is very openly dynamic and writing to it inside or outside of a component ends up being the same. So you can take Zustand's basic example...

1import create from "zustand";
2
3export const useBearStore = create((set) => ({
4  bears: 0,
5  increasePopulation: () => set((state) => ({ bears: state.bears + 1 })),
6  removeAllBears: () => set({ bears: 0 }),
7}))

...and create an effectively equivalent version with @deepsignal/preact like this...

1import { deepSignal } from "@deepsignal/preact";
2
3export const bearStore = {
4  data: deepSignal({
5    bears: 0
6  }),
7  increasePopulation() {
8    this.data.bears.value++;
9  },
10  removeAllBears() {
11    this.data.bears.value = 0
12  }
13};

Storing and fetching from localStorage

Because the value getter on a DeepSignal effectively calls the value getter on each underlying Signal, calling the DeepSignal's getter will properly subscribe to each underlying signal. So if you wanted to manage the side effects of any level of a DeepSignal you just need to call effect from @preact/signals and call DeepSignal.value

1import { deepSignal } from "@deepsignal/preact";
2import { effect } from "@preact/signals";
3
4type UserStore = {
5  name: {
6    first: string;
7    last: string;
8  };
9  email: string;
10}
11
12const getInitialUserStore = (): UserStore => {
13  const storedUserStore = localStorage.getItem("USER_STORE_KEY");
14  if (storedUserStore) {
15    // you should probably validate this 🤷‍♂️
16    return JSON.parse(storedUserStore);
17  } else {
18    return {
19      name: {
20        first: "",
21        last: ""
22      },
23      email: ""
24    };
25  }
26}
27
28const userStore = deepSignal(getInitialUserStore());
29
30effect(() => localStorage.setItem("USER_STORE_KEY", JSON.stringify(userStore.value)));

This would also work for any level of the DeepSignal.

1import { deepSignal } from "@deepsignal/preact";
2import { effect } from "@preact/signals";
3
4type UserNameStore = {
5  first: string;
6  last: string;
7};
8
9const getInitialUserNameStore = (): UserNameStore => {
10  const storedUserStore = localStorage.getItem("USER_NAME_STORE_KEY");
11
12  // you should probably validate this too 🤷‍♂️
13  return storedUserStore ? JSON.parse(storedUserStore) : { first: "", last: "" },
14}
15
16const userStore = deepSignal({
17  name: getInitialUserNameStore(),
18  email: ""
19});
20
21effect(() => localStorage.setItem("USER_NAME_STORE_KEY", JSON.stringify(userStore.name.value)));

This should fulfill most needs for middleware or plugins. If this fails to meet your needs, please file an issue and I will address the particular ask.

Modifiable Structure, new in 4.0.0

New in 4.0.0, you can now have DeepSignals that represent modifiable data structures. If you wanted to create a DeepSignal as a record, it could be modified using the following example.

1import { DeepSignalType, useDeepSignal } from "@deepsignal/preact";
2import { memo } from "preact/compat";
3
4export const TodoList = () => {
5  const store = useDeepSignal(() => ({
6    newItemName: "",
7    items: {} as Record<string, { name: string }>,
8  }));
9
10  return (
11    <>
12      <form
13        onSubmit={(e) => {
14          e.preventDefault();
15          store.items.value = {
16            ...store.items.peek(),
17            [Math.random().toString()]: { name: store.newItemName.peek() },
18          };
19          store.newItemName.value = "";
20        }}
21      >
22        <input
23          value={store.newItemName}
24          onInput={(e) => (store.newItemName.value = e.currentTarget.value)}
25        />
26        <button>Add new item</button>
27      </form>
28      <ul>
29        {Object.keys(store.items.value).map((id) => (
30          <TodoItem key={id} id={id} store={store} />
31        ))}
32      </ul>
33    </>
34  );
35};
36
37const TodoItem = memo(
38  ({
39    id,
40    store,
41  }: {
42    id: string;
43    store: DeepSignalType<{ items: Record<string, { name: string }> }>;
44  }) => (
45    <li>
46      {store.items[id].name}
47      <button
48        onClick={() => {
49          const items = { ...store.items.peek() };
50          delete items[id];
51          store.items.value = items;
52        }}
53        aria-label="Delete item"
54      >
55        ❌
56      </button>
57    </li>
58  )
59);

Possible footguns

It may appear that if you iterate over Object.keys(store.items) here, you can avoid unnecessary rerenders. However, you need to rely on rerenders to get updates to iterative mappings so you must map over Object.keys(store.items.value) and accept the VDOM rerenders. And thus, there isn't necessarily a huge gain in performance by storing data this way unless you only pass the key & store down to the iterated component and then memoize it to avoid unecessary rerenders.