micro-state

What

A really (856 byte gzipped) tiny state manager for React with hooks. Key-value based, global and performant (only refreshes a component if needed).

Why

I needed a simple state manager to use standalone or as a synchronous companion to react-query, that had the following characteristics:

• Small, no dependencies
• Global state (no prop drilling) without Connect, HOCs or boilerplate
• Tiny, hook-based API surface
• State can be modified or listened to from outside React, seamlessly
• Efficient: only triggers a refresh to a component if needed

Why not useReduce + React Context?

Because when context dispatches, it re-renders all the components that are subscribed to it. Also, it's not easy to access the store from outside React, which in some cases might be a problem - for example, when synchronising state externally between two different instances of the same web app.

How

To install

npm i --save @hya/micro-state

To use

import {
  useMicroState,
  StateClient,
  StateClientProvider,
} from "@hya/micro-state";

const client = new StateClient();

/* 
  External subscription to a key. This is completely optional.
  Keys can be externally set with .set (will trigger refresh)
  get with .get and checked for existence with .has 
*/

client.subscribe("counter", () =>
  console.log(client.has("counter"), client.get("counter"))
);

/* 
  StateClientProvider will guarantee that every descendant using useMicroState will trigger on key change
  with no additional configuration.
*/
function App() {
  return (
    <StateClientProvider client={client}>
      <CounterApp />
    </StateClientProvider>
  );
}

function CounterApp() {
  /* 
    useMicroState can work at any level below a Provider
    keys can be either arrays or string, but beware: ["my", "key"] is equivalent to "my.key"
    Components are refreshed only when the keys specified with useMicroState change.
  */

  const [counter, setCounter] = useMicroState("counter", 75);

  /*
    setter functions accept reducer functions or values, exactly like React's setState. 
  */
  return (
    <pre>
      <p>
        Counter: <strong>{counter}</strong>
      </p>
      <button onClick={() => setCounter((counter) => (counter -= 1))}>
        - 1
      </button>
      <button onClick={() => setCounter((counter) => (counter += 1))}>
        + 1
      </button>
      <button onClick={() => setCounter(0)}>Reset</button>
    </pre>
  );
}

export default App;

Reference

StateClient

const stateClient = new new StateClient()

When instantiated with new, creates an instance of a state client that can be used and/or passed to a StateClientProvider. This needs to be instantiated only once, typically outside of the root React component.

API

subscribe

stateClient.subscribe(key: Key, callback: ObserverCallback)

Subscribe to a key and call callback when the key is updated. Please note that the callback has no arguments and the key value won't be passed to the callback (use get to get it).

get

<T,>stateClient.get(key: Key): T

Get a key from the current state.

set

stateClient.set(key: Key, mutator: Mutator)

Set a key providing either a value or a mutator function (a function which takes the current value and returns the new value). This will trigger all the subscribers and refresh all the components using useMicroState for that key.

initialize

stateClient.initialize(providedKey: Key, value: unknown)

Set a key providing a value. This will not trigger any subscriber or refresh any component that uses useMicroState for that key.

has

<T,>stateClient.has(key: Key): boolean

Return true if key from the current state has been set or initialized once, false otherwise. This is useful because get will return undefined either for a key explicitly set to undefined or a key that was never set / initialized.

StateClientProvider

StateClientProvider({ client, children }: StateClientParams)

This is a React Context Provider that will allow the usage of useMicroState and useMicroStateClient in all its descendents. Gets passed a StateClient. Use it like this:

const client = new StateClient();

function MyApp() {
  return (
    <StateClientProvider client={client}>
      {/* All these children and their descendents will be able to use the hook methods */}
    </StateClientProvider>
  );
}

useMicroState

function useMicroState<T>(key: Key, initialValue: T): [T, MutatorFunction<T>]

Get a tuple containing the immediate value of the key key and a setter function that imperatively modifies the key like the stateClient.set method. If the value associated with the key is set, the component will refresh. This is typically the hook you want to use inside your react components.

Please note that:

• key can be a string or an array of strings | numbers. If it's an array, it will be internally serialized to a dot-separated string, so ["my", "array"] will be the same key as "my.array".

• The mutator function can either take a new value or a reducer function with the old value as only argument. In this last case, the returned value will be the new value, similarly to React's useState functional updates.

useMicroStateClient

function useMicroStateClient(): StateClient

A hook that returns the StateClient passed to the parent StateClientProvider. Useful to subscribe / unsubscribe to a key in a hook without refreshing the component (for example if we're using the key to update a canvas reference that's handled outside the React cycle and does its own repainting).