Zustand Optics

Zustand integration for optics-ts. Based on jotai-optics.

Install

npm i optics-ts @prncss-xyz/zustand-optics

Usage

First create a store

import { create } from "zustand";
import { withOptics } from "@prncss-xyz/zustand-optics";
import { optic } from "optics-ts";

const init = { bears: { grizzly: 0 } };
const useBearStore = withOptics(create(() => init));
const bearStoreO = optic<typeof init>();

Then

import { useCallback } from "react";

function GrizzlyCounter({ grizzly }: { grizzly: number }) {
  return <h1>{grizzly} around here...</h1>;
}
const grizzlyO = bearStoreO.prop("bears").prop("grizzly");

function App() {
  const [grizzly, setGrizzly] = useBearStore.rw(grizzlyO);
  const increasePopulation = useCallback(() => setGrizzly((x) => x + 1), [setGrizzly]);
  return (
    <>
      <GrizzlyCounter grizzly={grizzly} />
      <button onClick={increasePopulation}>one up</button>
    </>
  );
}

API

withOptics

const useStore = withOptics<S>(useBoundStore: UseBoundStore<StoreApi<S>>, defaultIsEqual = Object.is)

Create a hook with methods as described below. For the meaning of defaultIsEqual, see activate.

Basic hooks

get

const value = useStore.get(focus);

Returns the value of the focus. (Will return an array if focus is a traversable).

set

const setValue = useStore.set(focus);
setValue(value);

Returns a callback which accepts a value and sets the focus to it. If value is a value (!), sets the focus to that value. If value is a callback, applies the callback to focus. If value is undefined, removes the focus for a removable optics (prism and traversable) and do nothing otherwise.

The callback is stable.

Utility hooks

These are wrappers around the basic hooks which can help with code readability.

rw

Returns a pair made of the focus value and a set callback.

const [value, setValue] = useStore.rw(focus);

activate

const [active, activate] = useStore.activate(focus, target, isEqual?);
activate()

Returns a pair. The first value is a boolean representing whether the focus is equal to target. The second value is a callback setting focus to target value.

isEqual<A>(a: A, b: A): boolean

The second argument is an optional equality function. If not provided, it defaults to the second argument of createStoreWithOptics. If neither is provided, defaults to Object.is.

setWith

const setter = useStore.setWith([focus1, value1], [focus2, value2] /*, ...*/);
setter();

Creates a callback which calls multiple set operations from left to right.

Note on typing: if you have more than 7 arguments (please don't), TypeScript will assume they all have the same type.