React: Expected an assignment or function call and instead saw an expression

Question

I am trying to fix this lint error at line const def = (props) => { in following sample code.

const propTypes = {
prop1: PropTypes.string,
pr         


        

Answer 1

Possible way is (sure you can change array declaration to getting from db or another external resource):

const MyPosts = () => {

  let postsRawData = [
    { id: 1, text: 'Post 1', likesCount: '1' },
    { id: 2, text: 'Post 2', likesCount: '231' },
    { id: 3, text: 'Post 3', likesCount: '547' }
  ];

  const postsItems = []
  for (const [key, value] of postsRawData.entries()) {
    postsItems.push(<Post text={value.text} likesCount={value.likesCount} />)
  }

  return (
      <div className={css.posts}>Posts:
          {postsItems}
      </div>
  )
}

Answer 2

In my case the problem was the line with default instructions in switch block:

  handlePageChange = ({ btnType}) => {
    let { page } = this.state;
    switch (btnType) {
      case 'next':
        this.updatePage(page + 1);
        break;
      case 'prev':
        this.updatePage(page - 1);
        break;
      default: null;
    } 
  }

Instead of

default: null;

The line

default: ;

worked for me.

Answer 3

Expected an assignment or function call and instead saw an expression.

I had this similar error with this code:

const mapStateToProps = (state) => {
    players: state
}

To correct all I needed to do was add parenthesis around the curved brackets

const mapStateToProps = (state) => ({
    players: state
});

Answer 4

Not sure about solutions but a temporary workaround is to ask eslint to ignore it by adding the following on top of the problem line.

// eslint-disable-next-line @typescript-eslint/no-unused-expressions

Answer 5

You are not returning anything, at least from your snippet and comment.

const def = (props) => { <div></div> };

This is not returning anything, you are wrapping the body of the arrow function with curly braces but there is no return value.

const def = (props) => { return (<div></div>); }; OR const def = (props) => <div></div>;

These two solutions on the other hand are returning a valid React component. Keep also in mind that inside your jsx (as mentioned by @Adam) you can't have if ... else ... but only ternary operators.

Answer 6

You use a function component:

const def = (props) => {
<div>
<div className=" ..some classes..">{abc}</div>
<div className=" ..some classes..">{t('translation/something')}</div>

<div ...>
<someComponent 
 do something
/>

if (some condition) {
do this
} else {
do that
}

 </div>

};

In the function component, you have to write a return or just add parentheses. After the added return or parentheses your code should look like this:

const def = (props) => ({
<div>
<div className=" ..some classes..">{abc}</div>
<div className=" ..some classes..">{t('translation/something')}</div>

<div ...>
<someComponent 
 do something
/>

if (some condition) {
do this
} else {
do that
}

 </div>
});