🎣 React Context

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• TS/React docs: https://github.com/typescript-cheatsheets/react-typescript-cheatsheet#context

import { createContext } from 'react'

interface CurrentUserContextType {
  username: string
}

const CurrentUserContext = createContext<CurrentUserContextType | null>(null)

const useCurrentUser = () => {
  const currentUserContext = useContext(CurrentUserContext)

  if (!currentUserContext) {
    throw new Error(
      'useCurrentUser has to be used within <CurrentUserContext.Provider>'
    )
  }

  return currentUserContext
}

    

or this, but it’s not as good because it doesn’t provide the type safety that the above does:

export interface CurrentUserContextType {
  username: string
}

export const CurrentUserContext = createContext<CurrentUserContextType>(
  {} as CurrentUserContextType
)

    

Example Jump to heading

From this article

import * as React from 'react'

const CountContext = React.createContext()

function countReducer(state, action) {
  switch (action.type) {
    case 'increment': {
      return { count: state.count + 1 }
    }
    case 'decrement': {
      return { count: state.count - 1 }
    }
    default: {
      throw new Error(`Unhandled action type: ${action.type}`)
    }
  }
}

function CountProvider({ children }) {
  const [state, dispatch] = React.useReducer(countReducer, { count: 0 })
  // NOTE: you *might* need to memoize this value
  // Learn more in http://kcd.im/optimize-context
  const value = { state, dispatch }
  return <CountContext.Provider value={value}>{children}</CountContext.Provider>
}

function useCount() {
  const context = React.useContext(CountContext)
  if (context === undefined) {
    throw new Error('useCount must be used within a CountProvider')
  }
  return context
}

export { CountProvider, useCount }

    

Usage Jump to heading

import React, { useContext } from 'react'

const MyComponent = () => {
  const { count } = useCount()

  return <div>Count: {count}</div>
}

    

<CountProvider>
  <MyComponent />
</CountProvider>

    

Child as a function Jump to heading

We can change the CountProvider component

function CountProvider({ children }) {
  const [state, dispatch] = React.useReducer(countReducer, { count: 0 })
  const value = { state, dispatch }
  return (
    <CountContext.Provider value={value}>
      {children(value)}
    </CountContext.Provider>
  )
}

    

And use it like so:

<CountProvider>{({ count }) => <div>Count: {count}</div>}</CountProvider>

    

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