Expected 'this' to be used by class method

Question

In my class, eslint is complaining "Expected 'this' to be used by class method 'getUrlParams'

Here is my class:

class PostSearch extends React.Component {
  constructor(props) {
    super(props);
    this.getSearchResults();
  }

  getUrlParams(queryString) {
    const hashes = queryString.slice(queryString.indexOf('?') + 1).split('&');
    const params = {};

    hashes.forEach((hash) => {
      const [key, val] = hash.split('=');
      params[key] = decodeURIComponent(val);
    });

    return params;
  }

  getSearchResults() {
    const { terms, category } = this.getUrlParams(this.props.location.search);
    this.props.dispatch(Actions.fetchPostsSearchResults(terms, category));
  }

  render() {
    return (
      <div>
        <HorizontalLine />
        <div className="container">
          <Col md={9} xs={12}>
            <h1 className="aboutHeader">Test</h1>
          </Col>
          <Col md={3} xs={12}>
            <SideBar />
          </Col>
        </div>
      </div>
    );
  }
}

What is the best approach to solve this or refactor this component?

Answer 1

you should bind the function to this as the ESLint error says "Expected 'this' to be used by class method 'getUrlParams'

getUrlParams = (queryString) => { .... }

as you are not using getUrlParams during render (like onClick()) so the above technique is good which we can call it "usage of arrow function in class property".

there are other ways of binding too:

• binding in constructor this.getUrlParams=this.getUrlParams.bind(this)
• arrow function in render e.g.onClick={()=>this.getUrlParams()} assumed that function does not have params.
• and React.createClass which with ES6 does not make sense :)

Answer 2

getUrlParams = queryString => { ... }

Answer 3

My solution is to use this function outside of class and bind this function to class.

function getUrlParams(queryString) {
 const hashes = queryString.slice(queryString.indexOf('?') + 1).split('&');
 const params = {};
 hashes.forEach((hash) => {
  const [key, val] = hash.split('=');
  params[key] = decodeURIComponent(val);
 });
 return params;
}
class PostSearch extends React.Component {
  constructor(props) {
    super(props);
    this.getSearchResults();
    this.getUrlParams = getUrlParams.bind(this); // add this
  }

  getSearchResults() {
   const { terms, category } = this.getUrlParams(this.props.location.search);
   this.props.dispatch(Actions.fetchPostsSearchResults(terms, category));
  }
  render() {
   return (  "bla bla"  );
  }
}

Answer 4

A possible hack to this rule could be.

getMoviesByID(){
  //Add a reference to this in your function.
  this.funcName = 'getMoviesByID';
}

Answer 5

Another use case could be.

Let's say you have method called handlePasswordKeyUp. The body of function can be seen like this.

handlePasswordKeyUp() {
  console.log('yes')
}

Above code will trigger that error. So at least use this inside the body function

handlePasswordKeyUp(){
   this.setState({someState: someValue})
}

Answer 6

This is a ESlint rule, see class-methods-use-this.

You could extract the method getUrlParams and put it into a helper, or to make it static.

What could you also do is to move the this.props.location.search inside the method, therefore calling the this.getUrlParams() method without parameter, as it seems you are using it only once.

Therefore, this could look like:

getUrlParams() {
    const queryString = this.props.location.search;
    ...
    return params;
  }

A last option would be to disable this ESlint rule.