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:

``tsx
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(
useGetCounterValue,
defaultValue
)

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

return (


/**
* And use the generated Provider
*/
function App() {
return (



)
}
`

Installation

`
npm install react-generate-context
`

or

`
yarn add react-generate-context
`

API

`typescript
const [MyProvider, useMyContext] = generateContext(
useGetContextValue,
defaultValue
)
`

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

#### useGetContextValue

`typescript
type UseGetContextValue = (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:

`typescript
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:

`javascript
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 (

{children}


)
}
`

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`.