README.md

Context Creator

Installation

npm install context-creator

Usage

import contextCreator from 'context-creator'

function useValue (props: {
  initialCount: number
}) {
  const [count, setCount] = useState(props.initialCount)
  function increment () {
    setCount(current => current + 1)
  }
  const value = { count, increment }
  return value
}

export const {
  useContext: useCounter,
  Provider: CounterProvider, 
} = contextCreator({ name: 'counter', useValue })

function CounterConsumer () {
  const counter = useCounter()
  return (
    <>
      Count: {counter.count}
      <button onClick={counter.increment}>Increment</button>
    </>
  )
}

function App() {
  return (
    <CounterProvider initialCount={5}>
      <CounterConsumer />
    </CounterProvider>
  )
}

Problem

Creating and using React contexts out of the box requires repeating boilerplate code for each new context:

• defining a context type
• creating a context
• defining a hook to consume the context
• defining a provider component that wraps the internal context provider

Without Context Creator

context/counter.tsx

import { createContext, useContext } from 'react'

interface CounterContextValue {
  count: number
  increment: () => void
}

const counterContext = createContext<CounterContextValue | undefined>(undefined)

export function useCounter (): CounterContextValue {
  const value = useContext(counterContext)
  if (value == null) {
    const message = `useContext must be used within a Provider`
    throw new Error(message)
  }
  return value
}

export function CounterProvider (props: {
  initialCount: number
}): JSX.Element {
  const [count, setCount] = useState(props.initialCount)
  function increment () {
    setCount(current => current + 1)
  }
  const value = { count, increment }
  return (
    <createdContext.Provider value={value}>
      {providerProps.children}
    </createdContext.Provider>
  )
}

component/CounterConsumer.tsx

import { useCounter } from '../context/counter'

export default function CounterConsumer () {
  const counter = useCounter()
  return (
    <>
      Count: {counter.count}
      <button onClick={counter.increment}>Increment</button>
    </>
  )
}

App.tsx

import { CounterProvider } from './context/counter'
import CounterConsumer from './component/CounterConsumer'

export default function App() {
  return (
    <CounterProvider initialCount={5}>
      <CounterConsumer />
    </CounterProvider>
  )
}

Solution

Context creator minimizes this boilerplate. The contextCreator function defines the context, the provider, and consuming hooks for you. For TypeScript developers, it also infers the type of the context value and the provider's props.

You define a hook named useValue. The hook should take a single argument to receive the props passed to the created provider. contextCreator will infer the type of the created Provider's props from this argument. useValue's return value will be the passed to the internal context provider as it's value prop that can be consumed by any child component. contextCreator will infer the type of the created context's value from this return value. contextCreator also creates a hook that returns the provided context value or throw an error if called outside of a provider.

To create the provider and hooks, call contextCreator and pass a single object with two properties: name and useValue.

• name should be a string is used to identify the context in error messages.
• useValue should be a hook that will be called inside the provider. The provider's props will be passed to useValue, and whatever useValue returns will be provided to the context.

contextCreator will return an object of type ContextCreation. The object includes properties for the provider and hooks to consume the context. ContextCreation is a generic type that can be imported from the context-creator package. The functions contextCreator returns can be immediately destructured, aliased, and exported in a single statement.

With Context Creator

context/counter.ts

import contextCreator from 'context-creator'

function useValue (props: {
  initialCount: number
}) {
  const [count, setCount] = useState(props.initialCount)
  function increment () {
    setCount(current => current + 1)
  }
  const value = { count, increment }
  return value
}

export const {
  useContext: useCounter,
  Provider: CounterProvider
} = contextCreator({ name: 'counter', useValue })

component/CounterConsumer.tsx

import { useCounter} from '../context/counter'

export default function CounterConsumer () {
  const counter = useContext()
  return (
    <>
      Count: {counter.count}
      <button onClick={counter.increment}>Increment</button>
    </>
  )
}

App.tsx

import { CounterProvider } from './context/counter'
import CounterConsumer from './component/CounterConsumer'

export default function App() {
  return (
    <CounterProvider initialCount={5}>
      <CounterConsumer />
    </CounterProvider>
  )
}

Optional consumption

The created useContext hook will throw an error if used outside a provider. If you need to consume the context in a component that might be rendered outside a provider, call the useOptionalContext hook also returned by contextCreator.

import contextCreator from 'context-creator'

function useValue (props: {
  initialCount: number
}) {
  const [count, setCount] = useState(props.initialCount)
  const value = { count, setCount }
  return value
}

const {
  useContext: useCounter,
  useOptionalContext: useOptionalCounter,
  Provider: CounterProvider, 
} = contextCreator({ name: 'counter', useValue })

function RequiredConsumer () {
  const counter = useCounter()
  return <>Count: {counter.count}</>
}

function OptionalConsumer () {
  const counter = useOptionalCounter()
  if (counter == null) {
    return <>Unknown counter</>
  }
  return <>Count: {counter.count}</>
}

function App() {
  return (
    <>
      {/* Throws the error "(counter) useContext must be used within a Provider" */}
      <RequiredConsumer />


      {/* Renders "Unknown counter" with no error */}
      <OptionalConsumer />
    </>
  )
}