If you're using React Hook, UseEffect you can put the below changes in your component. It worked for me

useEffect(() => {
    window.addEventListener("beforeunload", alertUser);
    return () => {
      window.removeEventListener("beforeunload", alertUser);
    };
  }, []);
  const alertUser = (e) => {
    e.preventDefault();
    e.returnValue = "";
  };

It is actually quite straightforward, this will add the default alert whenever you reload your page.

In this answer you will find:

1. Default usage
2. Alert with validation

1. Default Usage

Functional Component

useEffect(() => {
    window.onbeforeunload = function() {
        return true;
    };

    return () => {
        window.onbeforeunload = null;
    };
}, []);

Class Component

componentDidMount(){
    window.onbeforeunload = function() {
        return true;
    };
}

componentDidUnmount(){
    window.onbeforeunload = null;
}

2. Alert with validation

You can put validation to only add alert whenever the condition is true.

Functional Component

useEffect(() => {
    if (condition) {
        window.onbeforeunload = function() {
            return true;
        };
    }

    return () => {
        window.onbeforeunload = null;
    };
}, [condition]);

Class Component

componentDidMount(){
    if (condition) {
        window.onbeforeunload = function() {
            return true;
        };
    }
}

componentDidUnmount(){
    window.onbeforeunload = null;
}

Unfortunately currently accepted answer cannot be more considered as acceptable since performance.navigation.type is deprecated

The newest API for that is experimental ATM. As a workaround I can only suggest to save some value in redux (or whatever you use) store to indicate state after reload and on first route change update it to indicate that route was changed not because of refresh.

Your code seems to be working just fine, your alert won't work because you aren't stopping the refresh. If you console.log('hello') the output is shown.

UPDATE ---

This should stop the user refreshing but it depends on what you want to happen.

componentDidMount() {
    window.onbeforeunload = function() {
        this.onUnload();
        return "";
    }.bind(this);
}

If you are using either REDUX or CONTEXT API then its quite easy. You can check the REDUX or CONTEXT state variables. When the user refreshes the page it reset the CONTEXT or REDUX state and you have to set them manually again. So if they are not set or equal to the initial value which you have given then you can assume that the page is refreshed.

'navigation' is deprecated, instead, add this to the constructor:

const navigationEntries = window.performance.getEntriesByType('navigation');
if (navigationEntries.length > 0 && navigationEntries[0].type === 'reload') {
 console.log("Page was reloaded");
}

Make sure to wrap it in the useEffect(). The reason for using useEffect in this case is to ensure that the code runs at the appropriate time during the component lifecycle.

When you place the code directly inside the function body without useEffect, it will be executed whenever the component function is called, which could lead to unexpected behavior.

By using useEffect with an empty dependency array ([]), you ensure that the code runs only once, after the initial render of the component. This approach is generally preferred when you want to perform initialization tasks or set up event listeners in a React component.

function MyComponent(){

   useEffect(() => {
     const navigationEntries = window.performance.getEntriesByType('navigation');
     if (navigationEntries.length > 0 && navigationEntries[0].type === 'reload') {
       console.log("Page was reloaded");
     }
   }, []);

}

export default MyComponent;

If you're using react-router-dom you can use this approach:

import { useHistory } from 'react-router-dom';    
const history = useHistory();

if(history.action === 'POP'){
  console.log('Refreshed or used back/forward navigation')
}