Create-global-context NPM

Better way to work with React Context,

The create-global-context way!

NPM

Compatible with React v17 and above

The why?

Wanting to have react components in sync with each other could be a little overwhelming sometimes. We could lift up the state and drift the state down the component tree recursively through component props till we get the state down to where we desire prop-drilling.

Here is where React Context comes to play, by keeping all pages and components in sync. But the problem with React Context is that when not used with caution it can be quite confusing. For example, when the context changes, the the useContext will cause a re-render even if the component is not using the changed value, causing performance issues.

There are many solutions to this problem, but the preferred solution is to split the context. This is where you would need to put variables that change a lot into a different context, this way you can have some optimization as not all components using context will re-render, since the components will be using different context. This could mean having many different contexts and many providers around your App component, which could be a bit messy in my opinion.

The reason for this solution create-global-context is to have one Context and one Provider. To make sure that all components do not re-render and only re-render those components which are using the value from the context which has changed. This is achieved by using selectors.

Getting Started

The Package can be installed from NPM

npm i create-global-context

npm install create-global-context

yarn add create-global-context

Usage

import { createGlobalContext } from 'create-global-context'

The second step is to create a global context

createGlobalContext takes one argument; which is the initial state, or the shape of the state. createGlobalContext returns a Provider component wrapper which wraps around components which will be using the context, and useStore hook to get and modify the state.

const { Provider, useStore } = createGlobalContext({ name: 'Context', id: 1, count: 1 })

The third step is to use the Provider

wrap the Provider around components which will be using the context.

function App() {
  return (
    <Provider>
      <>
        <NameComponent />
        <Count />
      </>
    </Provider>
  )
}

Finally step four; we use the useStore.

in order to get the store or make changes to the store we will be using useStore hook returned by the createGlobalContext fn in step 2. useStore hook returns a tuple, index 0 is the state itself, index 1 is the setter function.

without the setter function

const NameComponent = () => {
  const [state] = useStore()
  return <div>{state.name}</div>
}

with setter function

const Count = () => {
  const [state, setStore] = useStore()
  return (
    <div>
      <p>{state.count}</p>
      <button onClick={() => setStore({ count: state.count + 1 })}>ADD</button>
    </div>
  )
}

The setStore function returned by useStore hook can be used in two ways. First way to pas in the object with what you want to change or update and second way is to pass in a callback function which takes the current state as the first argument. Very similar behavior to useState hook.

First Method

<button onClick={() => setStore({ count: state.count + 1 })}>ADD</button>

Second Method

<button onClick={() => setStore((currentState) => ({ count: currentState.count + 1 }))}>ADD</button>

Usage with Reducers

You also have the ability to use reducers while working with context created with createGlobalContext. In order to achieve this, you need to pass reducer as the second argument to createGlobalContext; i.e. createGlobalContext({ name: 'Context', id: 1, count: 1 }, reducer). The reducer of course has to be of type function and takes two arguments; the first argument is the state and the second argument is the action. Below is an example of how it works;

type Action = { type: 'increment' } | { type: 'decrement' } | { type: 'reset'; payload: number };

function reducer(state: State, action: Action) {
   switch (action.type) {
      case 'increment':
         return { ...state, count: state.count + 1 };
      case 'decrement':
         return { ...state, count: state.count - 1 };
      case 'reset':
         return { ...state, count: action.payload };
      default:
         throw new Error();
   }
}

To display the state and set to the state:

function Counter() {
   const [count, dispatch] = useStore((state) => state.count);
   return (
      <>
         <p> Count: {count}</p>
         <button onClick={() => dispatch({ type: 'reset', payload: 0 })}>Reset</button>
         <button onClick={() => dispatch({ type: 'decrement' })}>-</button>
         <button onClick={() => dispatch({ type: 'increment' })}>+</button>
      </>
   );
}

useStore also supports selectors while working with reducers. Just pass in a callback to useStore to select something specific from the store. if you do not pass in a cb to useStore, the whole state will be returned, and on any state change, component will re-render.

Updating the Store

If you have a component which DOESN'T use the store but does set to the store, then you should use the useSet hook returned by createGlobalContext, this is to avoid the re-render of the component.

:warning: It also works with Reducers.

const { Provider, useStore, useSet, useDispatch } = createGlobalContext({ name: 'Context', id: 1, count: 1 });

The useSet and useDispatch hook returns a function which behaves similar to the setter function returned by useStore.

const CountWithSet = () => {
   const set = useSet();
   return <button onClick={() => set({ count: 2000 })}>ADD</button>;
};

You can either invoke the function with partial state like in the example above, or you can set to the store by passing in a callback function which takes the current state as argument which returns the partial state which will be merged with the current state in the store.

const CountWithSet = () => {
   const set = useSet();
   return <button onClick={() => set((currentState) => ({ count: currentState.count + 2 }))}>ADD</button>;
};

useDispatch

const ChildWithDispatch = () => {
   const dispatch = useDispatch();
   return <button onClick={() => dispatch({ type: 'increment' })}>ADD</button>;
};

With reducer context, it would look like this: <button onClick={() => set({ type: 'decrement' })}>ADD</button> For more info on reducers see docs/reducer-context.md. Reducer Docs

Avoiding unnecessary re-renders - Selectors

In order to avoid the unnecessary re-renders there is one more step to follow. Quite Simply pass in a callback function to the useStore hook to get what we want from the store instead of the whole store state itself, which will cause a re-render and we do not want that. By using selectors the component will only render if that the piece of state changes to which that specific component is being subscribed to.

Step 4 from `Usage` would look something like this;

without setter function

const NameComponent = () => {
  const [name] = useStore((state => state.name))
  return <div>{name}</div>
}

with setter function

const Count = () => {
  const [count, setStore] = useStore((state) => state.count)
  return (
    <div>
      <p>{count}</p>
      <button onClick={() => setStore((currentState) => ({ count: currentState.count + 1 }))}>ADD</button>
    </div>
  )
}