really minimal wrap on new React.createContext() to provide context with a set function for Consumer

NOTE

According to 0002-new-version-of-context, mutation is discouraged. But in some situations, Consumer really need a way to update the Provider. So, I come up with this module.

Usage

import createMutableContext from 'create-mutable-context'

const { Provider, Consumer } = createMutableContext()

<Provider defaultValue={1}>
  <Consumer>
    {ctx => {
      // ctx contain value and a set function
      return (
        <button onClick={() => ctx.set(ctx.value + 1)}>
          {ctx.value}
        </button>
      )
    }}
  </Consumer>
</Provider>

ctx.set()

set(updater[, callback])

set function interface is similar to react component's setState(), which accept updater as object or function.

updater as function with the signature:

(prevValue, providerProps) => newValue

set will just replace the value. It will NOT merge newValue to prevValue.

keep value in your own state by Provider.onChange

you can also keep value in your own state (like Input)

import createMutableContext from 'create-mutable-context'

const { Provider, Consumer } = createMutableContext()

class App extends React.Component {
  state = { valueA: 1 }
  render() {
    return (
      <Provider
        value={this.state.valueA}
        onChange={valueA => this.setState({ valueA })}
      >
      ...
      </Provider>
    )
  }
}

access via ctx.foo instead ctx.value.foo

Can use createStateMutext to mutate whole provider state instead of a value field only.

import { createStateMutext } from 'create-mutable-context'

const C = createStateMutext({ foo: 1 })

const App = () => (
  <C.Provider>
    <C.Consumer>
      {ctx => (
        <button
          onClick={() => ctx.set({ foo: ctx.foo + 1 })}
        >
          {ctx.foo}
        </button>
      )}
    </C.Consumer>
  </C.Provider>
)

createObservableMutext

Consumers can observe part of changes easily by names. Names are auto calculate to bitmask

import { createObservableMutext } from 'create-mutable-context'

const C = createObservableMutext({ foo: 0, bar: 0 }, { foo: {}, bar: {} })

const App = () => (
  <C.Provider>
    <C.Consumer
      // observe to foo and only render if foo is changed
      observe="foo"
    >
      {ctx => `Foo: ${ctx.foo}`}
    </C.Consumer>
    <C.Consumer
      // observe to bar and only render if bar is changed
      observe="bar"
    >
      {ctx => `Bar: ${ctx.bar}`}
    </C.Consumer>
    <C.Consumer
      // observe to bar OR foo and render if bar OR foo are changed
      observe="bar,foo"
    >
      {ctx => `BarOrFoo: ${ctx.bar} ${ctx.foo}`}
    </C.Consumer>
  </C.Provider>
)

use option to add functions to ctx

createMutableContext signature:

import createMutableContext from 'create-mutable-context'

const options = {
  // init at the end of provider constructor
  providerConstruct: (provider) => {},

  // init at the end of consumer constructor
  consumerConstruct: (consumer) => {},

  // prepare ctx to pass to consumer children function
  consumerCtx: (ctx, consumer) => ctx,
}
createMutableContext(defaultValue, calculateChangedBits, option)

const C = createMutableContext(defaultValue, null, {
  providerConstruct(provider) {
    Object.assign(provider.state, {
      inc1() {
        this.set(prevState => { value: prevState.value + 1 })
      }
    })
  },  
})

const App = () => (
  <C.Provider>
    <C.Consumer>
      {ctx => (
        <button
          // can call inc1
          onClick={ctx.inc1}
        >
          {ctx.value}
        </button>
      )}
    </C.Consumer>
  </C.Provider>
)