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100 lines
2.4 KiB
100 lines
2.4 KiB
# create-react-context
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> Polyfill for the [proposed React context API](https://github.com/reactjs/rfcs/pull/2)
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## Install
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```sh
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yarn add create-react-context
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```
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You'll need to also have `react` and `prop-types` installed.
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## API
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```js
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const Context = createReactContext(defaultValue);
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// <Context.Provider value={providedValue}>{children}</Context.Provider>
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// ...
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// <Context.Consumer>{value => children}</Context.Consumer>
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```
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## Example
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```js
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// @flow
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import React, { type Node } from 'react';
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import createReactContext, { type Context } from 'create-react-context';
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type Theme = 'light' | 'dark';
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// Pass a default theme to ensure type correctness
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const ThemeContext: Context<Theme> = createReactContext('light');
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class ThemeToggler extends React.Component<
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{ children: Node },
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{ theme: Theme }
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> {
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state = { theme: 'light' };
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render() {
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return (
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// Pass the current context value to the Provider's `value` prop.
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// Changes are detected using strict comparison (Object.is)
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<ThemeContext.Provider value={this.state.theme}>
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<button
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onClick={() => {
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this.setState(state => ({
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theme: state.theme === 'light' ? 'dark' : 'light'
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}));
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}}
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>
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Toggle theme
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</button>
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{this.props.children}
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</ThemeContext.Provider>
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);
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}
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}
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class Title extends React.Component<{ children: Node }> {
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render() {
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return (
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// The Consumer uses a render prop API. Avoids conflicts in the
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// props namespace.
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<ThemeContext.Consumer>
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{theme => (
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<h1 style={{ color: theme === 'light' ? '#000' : '#fff' }}>
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{this.props.children}
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</h1>
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)}
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</ThemeContext.Consumer>
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);
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}
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}
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```
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## Compatibility
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This package only "ponyfills" the `React.createContext` API, not other
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unrelated React 16+ APIs. If you are using a version of React <16, keep
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in mind that you can only use features available in that version.
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For example, you cannot pass children types aren't valid pre React 16:
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```js
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<Context.Provider>
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<div/>
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<div/>
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</Context.Provider>
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```
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It will throw `A valid React element (or null) must be returned. You may have returned undefined, an array or some other invalid object.` because `<Context.Provider>` can only receive a single child element. To fix the error just wrap everyting in a single `<div>`:
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```js
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<Context.Provider>
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<div>
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<div/>
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<div/>
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</div>
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</Context.Provider>
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```
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