javascript - Function not defined error in React.JS component class - Stack Overflow

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I have written a react ponent with a constructor, methods, and render. When I ment out the methods and have only the render and constructor everything is fine, but when I add the methods the first always es up as undefined unless I close off the whole class after the constructor.

Here is my class (since it doesn't matter what is in the methods I just put the declarations for brevity):

export default class App extends Component {

  constructor(props) {
    super(props);
    const allWords = ["word", "pipe", "dear", "deer", "fish", "coat"];
    const word= allWords[Math.floor(Math.random()*allWords.length)];
    var lettersFound = [];
    for (var i=0; i<word.length;i++) {
      lettersFound = [...lettersFound, [i, "_"]];
    }
    this.fillWord = this.fillWord.bind(this);

    this.state = {
      word: word,
      numWrongGuesses: 0,
      lettersGuessed: [],
      lettersFound: lettersFound,
      error: ""
    }
  }

  isLetterInWord = (letter) => {
  }

  fillWord = () => {
  }



  handleGuess = (letter) => {
  }

  render () {
    return (
      <div className="App">
      </div>
    );
  }

}

This doesn't pile, giving the error "'isLetterInWord' is not defined". If I remove this function, the error is thrown on fillWord instead. If I add a "}" after the constructor the methods are all defined but render throws an unexpected token error on the return line. I do not understand why I would want to close off the class after the constructor, or why it isn't piling as is.

I have written a react ponent with a constructor, methods, and render. When I ment out the methods and have only the render and constructor everything is fine, but when I add the methods the first always es up as undefined unless I close off the whole class after the constructor.

Here is my class (since it doesn't matter what is in the methods I just put the declarations for brevity):

export default class App extends Component {

  constructor(props) {
    super(props);
    const allWords = ["word", "pipe", "dear", "deer", "fish", "coat"];
    const word= allWords[Math.floor(Math.random()*allWords.length)];
    var lettersFound = [];
    for (var i=0; i<word.length;i++) {
      lettersFound = [...lettersFound, [i, "_"]];
    }
    this.fillWord = this.fillWord.bind(this);

    this.state = {
      word: word,
      numWrongGuesses: 0,
      lettersGuessed: [],
      lettersFound: lettersFound,
      error: ""
    }
  }

  isLetterInWord = (letter) => {
  }

  fillWord = () => {
  }



  handleGuess = (letter) => {
  }

  render () {
    return (
      <div className="App">
      </div>
    );
  }

}

This doesn't pile, giving the error "'isLetterInWord' is not defined". If I remove this function, the error is thrown on fillWord instead. If I add a "}" after the constructor the methods are all defined but render throws an unexpected token error on the return line. I do not understand why I would want to close off the class after the constructor, or why it isn't piling as is.

• javascript
• reactjs

Share Improve this question Follow asked May 4, 2019 at 20:15 Heather FrankHeather Frank 14533 silver badges88 bronze badges 5

• how do you call the isLetterInWord method ? – Olivier Boissé Commented May 4, 2019 at 20:30
• Running your code in this sandbox: codesandbox.io/s/zxpnk301pl. It doesnt seem to be giving any errors. – Cat_Enthusiast Commented May 4, 2019 at 20:32
• 2 maybe this plugin babeljs.io/docs/en/babel-plugin-proposal-class-properties in missing in his babel config – Olivier Boissé Commented May 4, 2019 at 20:39
• @OlivierBoissé I call the method in another method just as isLetterInWord(letter); That plug-in didn't seem to help. It's strange, before I added the isLetterInWord() the other functions worked just fine. Now I have this issue. – Heather Frank Commented May 5, 2019 at 23:49
• @ChristopherNgo it worked just fine until I added isLetterInWord in my browsers. It's very strange. – Heather Frank Commented May 5, 2019 at 23:56

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 5

Try to bind the function inside the constructor like this:

this.isLetterInWord = this.isLetterInWord.bind(this);
this.fillWord = this.fillWord.bind(this)
this.handleGuess = this.handleGuess.bind(this);

Here you are defining class properties, which is currently (I think) is stage-3 proposal. In other words it is not supported by default. May be because of this you are getting errors. You can use class-properties-transform plugin for Babel to add support of this syntax though if you want to .

isLetterInWord = (letter) => {
  }

  fillWord = () => {

  }

Try defining methods as and see if it works

isLetterInWord(letter) {

}

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