// Assuming the error is referring to a missing static flag in a component

​

// Incorrect component definition

class MyComponent extends React.Component {

  // ...component code

}

​

// Correct component definition with static flag

class MyComponent extends React.Component {

  static myFlag = true;

  // ...component code

}

//If condition must be after useEffet()

// error

const C = () =>  {

    if (condition) return null;

    useEffect(() => {/*...*/}, []);

    return <div></div>

}

​

//no error

const C = () =>  {

    useEffect(() => {/*...*/}, []);

    if (condition) return null;

    return <div></div>

}