react-generate-context

React Context with less boilerplate.

Creating a new React Context involves a few steps. react-generate-context removes a couple of those steps.

The react-generate-context package is a single function, generateContext, that generates a React Context (in closure) and returns to you the Provider and custom hook to access it in one step. All you need to do is give it a function that creates and updates the value prop for your Context. Let's go through an example:

import generateContext from 'react-generate-context'

type Context = [
  number,
  {
    inc: () => void
    dec: () => void
  }
]

type Props = {
  startingCount: number
}

/**
 * `generateContext` receives a custom hook function that manages the `value`
 * passed to the Provider under the hood. The function takes any `props` passed
 * to the Provider
 */
const useGetCounterValue = ({ startingCount }: Props): Context => {
  const [state, setState] = React.useState(startingCount)
  const handlers = React.useMemo(
    () => ({
      inc: () => {
        setState(s => s + 1)
      },
      dec: () => {
        setState(s => s - 1)
      },
    }),
    []
  )

  return [state, handlers]
}

/**
 * An optional defaultValue can be passed to the underlying `createContext` function
 */
const defaultValue: Context = [
  0,
  {
    inc: () => {},
    dec: () => {},
  },
]

/**
 * generateContext returns a tuple of a Provider and a custom
 * hook to consume the context. Array destructuring allows you
 * to name the Provider and hook whatever you need to easily
 */
const [CounterProvider, useCounter] = generateContext<Context, Props>(
  useGetCounterValue,
  defaultValue
)

/**
 * We can consume that context in a component with the hook
 */
function Counter() {
  const [count, { inc, dec }] = useCounter()

  return (
    <div>
      {count}
      <div>
        <button onClick={inc}>+</button>
        <button onClick={dec}>-</button>
      </div>
    </div>
  )
}

/**
 * And use the generated Provider
 */
function App() {
  return (
    <CounterProvider startingCount={100}>
      <Counter />
    </CounterProvider>
  )
}

Installation

npm install react-generate-context

or

yarn add react-generate-context

API

const [MyProvider, useMyContext] = generateContext<Context, Props>(
  useGetContextValue,
  defaultValue
)

generateContext receives two arguments: useGetContextValue and an optional defaultValue for your Context.

useGetContextValue

type UseGetContextValue<Props, Context> = (props: Props) => Context

The useGetContextValue is a custom hook function that derives the value of your context. It is given any props passed to the Provider.

Example:

type Props = {
  startingCount: number
}

type Context = [
  number,
  {
    inc: () => void
    dec: () => void
  }
]

const useGetCounterValue = ({ startingCount }: Props): Context => {
  const [state, setState] = React.useState(startingCount)
  const handlers = React.useMemo(
    () => ({
      inc: () => {
        setState(s => s + 1)
      },
      dec: () => {
        setState(s => s - 1)
      },
    }),
    []
  )

  return [state, handlers]
}

defaultValue

defaultValue is the value utilized by the Context when a Consumer is rendered without a Provider as a parent. It is passed to React.createContext under the hood.

Why?

Reducing boilerplate aside, there's one other good reason to use a helper like generateContext when creating Contexts (or at least follow the pattern of its Provider).

The Provider returned to you does not allow you to put any components or elements in the same scope where the state change for the context is occurring. This prevents you from making a mistake that causes unnecessary rerendering. For example:

import React from 'react'
import SomeOtherFeature from './SomeOtherFeature'
import useManageValue from './useManageValue'

const defaultValue = {}

const MyContext = React.createContext(defaultValue)
const useMyContext = () => React.useContext(MyContext)

const MyProvider = ({ children }) => {
  const value = useManageValue()

  return (
    <MyContext.Provider value={value}>
      {children}
      <SomeOtherFeature />
    </MyContext.Provider>
  )
}

In this instance, because we have composed SomeOtherFeature in the same scope as where our state change for value occurs, no matter what you do to SomeOtherFeature, even if it doesn't consume useMyContext, it will be rerendered every time value changes.

The Provider returned to you by generateContext only allows you to use it with composition via children. It ensures that no mistake like the one above can be made now or in the future. Your Provider will work as well as it can. The onus is still on you to write a good custom hook to manage the value.