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HTML

              
                <div id="root"></div>
              
            
!

CSS

              
                
              
            
!

JS

              
                
// Contextを生成する
const NumberContext = React.createContext();
// 2つの値を持つオブジェクトを返す
// { Provider, Consumer }

const App = () => {
  // Providerを活用して値を全ての
  // 子要素と孫要素に利用可能にする
  return (
    <NumberContext.Provider value={42}>
      <div>
        <Display />
      </div>
    </NumberContext.Provider>
  );
}

const Display = () => {
  // Consumerを活用してcontextから取得した値を使う
  // このコンポーネントはpropsを取らないことに注意!
  return (
    <NumberContext.Consumer>
      {value => <div>親コンポーネントから渡された値: {value}</div>}
    </NumberContext.Consumer>
  );
}

ReactDOM.render(<App />, document.getElementById("root"));
              
            
!
999px

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