React：Uncaught TypeError：ヌルの 'sendTranslation'プロパティを読み取ることができません

Question

なぜこのエラーが発生するのかわかりません。私はちょうどthis.sendTranslationと呼ぶ。私はそれがe.preventDefault()行だったかもしれないと思ったが、そうではない。何が問題なのですか。sendTranslationをPopup.checkIfEnterPressedから電話するにはどうすればよいですか？

import React from "react"; 
import "../../styles/popup.css"; 

export default class Popup extends React.Component { 
    constructor(props) { 
    super(props); 

    // STATE 
    this.state = { 
     word: "", 
     translation: "" 
    }; 
    // BINDINGS 
    this.handleChange = this.handleChange.bind(this); 
    this.sendTranslation = this.sendTranslation.bind(this); 
    } 

    sendTranslation() { 
    // send translation to background.js 
    chrome.runtime.sendMessage(
     { wordsPair: [this.state.word, this.state.translation] }, 
     function(response) { 
     window.close(); 
     } 
    ); 
    } 

    checkIfEnterPressed(e) { 
    if (e.keyCode == 13) { 
     e.preventDefault(); // to prevent calling handleChange 
     this.sendTranslation(); 
    } 
    } 

    handleChange(e) { 
    const name = e.target.name; 

    this.setState({ 
     [name]: e.target.value 
    }); 
    } 

    render() { 
    return (
     <div id="container"> 
     <header>Fishky</header> 
     <div className="word field"> 
      <input 
      type="text" 
      name="word" 
      placeholder="Word" 
      value={this.state.word} 
      onKeyUp={this.checkIfEnterPressed} 
      onChange={this.handleChange} 
      /> 
     </div> 
     <div className="translation field"> 
      <input 
      type="text" 
      name="translation" 
      placeholder="Translation/Definition" 
      value={this.state.translation} 
      onKeyUp={this.checkIfEnterPressed} 
      onChange={this.handleChange} 
      /> 
     </div> 
     <div className="submit-word"> 
      <button 
      type="button" 
      className="btn btn-default btn-block" 
      id="submit-popup" 
      onClick={this.sendTranslation} 
      > 
      add 
      </button> 
     </div> 
     </div> 
    ); 
    } 
} 

エラー。なぜnullになるのですか？

Uncaught TypeError: Cannot read property 'sendTranslation' of null 
    at checkIfEnterPressed (Popup.js:31) 
    at Object.ReactErrorUtils.invokeGuardedCallback (ReactErrorUtils.js:69) 
    at executeDispatch (EventPluginUtils.js:85) 
    at Object.executeDispatchesInOrder (EventPluginUtils.js:108) 
    at executeDispatchesAndRelease (EventPluginHub.js:43) 
    at executeDispatchesAndReleaseTopLevel (EventPluginHub.js:54) 
    at Array.forEach (<anonymous>) 
    at forEachAccumulated (forEachAccumulated.js:24) 
    at Object.processEventQueue (EventPluginHub.js:254) 
    at runEventQueueInBatch (ReactEventEmitterMixin.js:17) 

Answer 1

また、この方法でバインドする必要があります。checkIfEnterPressed

constructor(props) { 
     super(props); 

     // STATE 
     this.state = { 
     word: "", 
     translation: "" 
     }; 
     // BINDINGS 
     this.handleChange = this.handleChange.bind(this); 
     this.sendTranslation = this.sendTranslation.bind(this); 
     this.checkIfEnterPressed = this.checkIfEnterPressed.bind(this); 
    } 

を