In React Router v6, how to check form is dirty before leaving page/route

Question

Below are the package versions I'm using.

React version - 16.13.1
react-router-dom version - 6.0.0-beta.0
react-redux version 7.2.0
Material UI version 4.11.0

How/what is the best way to check that a form isDirty (has changed) when the user is trying to leave the current page? I would like to prompt "Are you sure want to leave...." if the form isDirty.

I will fetch the data from within useEffect() and use a redux reducer to render the UI.

Should I declare a variable to keep the original fetched data for dirty checking?

This is what I am doing, but it is not working correctly.

component.js

 useEffect(() => {
    props.fetchUserInfo();
 })

action.js

export function fetchUserInfo() {
 return (dispatch) => {
     dispatch({type: USER_INITIALSTATE, {Name: 'abc', Age: 20}} 
     )
 }
}

userReducer.js

const initialState = {
  processing: false,
  success: false,
  fail: false,
  Profile: {}
}
let oriState;
let State;
const UserReducer = (state = initialState, action) => {
  if (action.type === USER_INITIALSTATE) {
    oriState = {Profile: action.data};
    State = {...state, Profile: action.data};
    return {...state, Profile: action.data};
  } else if (action.type === OTHERS_ACTION) {
     //update field change
     return {...state, xxx}
  }
}
export const userIsDirty = state => {
  if (oriState && State) {
    return JSON.stringify(oriState.Profile) !== JSON.stringify(State.Profile);
  }
  return false;
};
export default UserReducer;

So in my component I call userIsDirty to return the isDirty boolean, but I haven't figured out how to catch the leave page event and use this as a trigger to do the dirty form checking.

So how to detect leaving the current page? I tried something on useEffect return(component umount), but the props is not getting the updated INITIALSTATE state (meaning I will get Profile: {}), because it only runs once, but if I add the useEffect optional array argument, I get an infinite loop(maybe I set it wrong?).

useEffect(() => {
    props.fetchUserInfo();
    return () => {
      console.log(props); //not getting initial state object
    };
  }, []);

Am I doing this the correct way? What have I missed? Is there a better/correct solution to achieve what I want?

Thanks @gdh, useBlocker is the one I want. I am using it to popup a confirmation dialog.

I will share my complete codesandbox, I believe this may be helpful for someone in the future.

show confirmation dialog by using useBlocker

Answer 1

Just adding an additional answer for React Router v6 users.

As of v6.0.0-beta - useBlocker and usePrompt were removed (to be added back in at a later date).

It was suggsested if we need them in v6.0.2 (current version at the time of writing) that we should use existing code as an example.

Here is the code directly from the the alpha for these hooks.

So to add the hooks back in would be this code (anywhere in your app for usage): ** I only copied the code for react-router-dom - if you're using native, then you'll need to check the above link for the other usePrompt hook

/**
 * These hooks re-implement the now removed useBlocker and usePrompt hooks in 'react-router-dom'.
 * Thanks for the idea @piecyk https://github.com/remix-run/react-router/issues/8139#issuecomment-953816315
 * Source: https://github.com/remix-run/react-router/commit/256cad70d3fd4500b1abcfea66f3ee622fb90874#diff-b60f1a2d4276b2a605c05e19816634111de2e8a4186fe9dd7de8e344b65ed4d3L344-L381
 */
import { useContext, useEffect, useCallback } from 'react';
import { UNSAFE_NavigationContext as NavigationContext } from 'react-router-dom';
/**
 * Blocks all navigation attempts. This is useful for preventing the page from
 * changing until some condition is met, like saving form data.
 *
 * @param  blocker
 * @param  when
 * @see https://reactrouter.com/api/useBlocker
 */
export function useBlocker( blocker, when = true ) {
    const { navigator } = useContext( NavigationContext );

    useEffect( () => {
        if ( ! when ) return;

        const unblock = navigator.block( ( tx ) => {
            const autoUnblockingTx = {
                ...tx,
                retry() {
                    // Automatically unblock the transition so it can play all the way
                    // through before retrying it. TODO: Figure out how to re-enable
                    // this block if the transition is cancelled for some reason.
                    unblock();
                    tx.retry();
                },
            };

            blocker( autoUnblockingTx );
        } );

        return unblock;
    }, [ navigator, blocker, when ] );
}
/**
 * Prompts the user with an Alert before they leave the current screen.
 *
 * @param  message
 * @param  when
 */
export function usePrompt( message, when = true ) {
    const blocker = useCallback(
        ( tx ) => {
            // eslint-disable-next-line no-alert
            if ( window.confirm( message ) ) tx.retry();
        },
        [ message ]
    );

    useBlocker( blocker, when );
}

Then the usage would be:

const MyComponent = () => {
    const formIsDirty = true; // Condition to trigger the prompt.
    usePrompt( 'Leave screen?', formIsDirty );
    return (
        <div>Hello world</div> 
    );
};

Answer 2

Update:

Prompt, usePrompt and useBlocker have been removed from react-router-dom. This answer will not currently work, though this might change. The github issue, opened Oct 2021, is here

The answer...

This answer uses router v6.

1. You can use usePrompt.

• usePrompt will show the confirm modal/popup when you go to another route i.e. on mount.
• A generic alert with message when you try to close the browser. It handles beforeunload internally

usePrompt("Hello from usePrompt -- Are you sure you want to leave?", isBlocking);

2. You can use useBlocker

• useBlocker will simply block user when attempting to navigating away i.e. on unmount
• A generic alert with message when you try to close the browser. It handles beforeunload internally

useBlocker(
    () => "Hello from useBlocker -- are you sure you want to leave?",
    isBlocking
  );

Demo for both 1 & 2

3. You can also use beforeunload. But you have to do your own logic. See an example here