TypeScript version of https://betterprogramming.pub/prevent-route-changes-and-unsaved-data-loss-in-next-js-f93622d73791

useLeavePageConfirmation.ts

import SingletonRouter, { Router } from 'next/router';
import { useEffect } from 'react';

const defaultConfirmationDialog = async (msg?: string) => window.confirm(msg);

/**
 * Inspiration from: https://stackoverflow.com/a/70759912/2592233
 */
export const useLeavePageConfirmation = (
  shouldPreventLeaving: boolean,
  message: string = 'Changes you made may not be saved.',
  confirmationDialog: (msg?: string) => Promise<boolean> = defaultConfirmationDialog
) => {
  useEffect(() => {
    // @ts-ignore because "change" is private in Next.js
    if (!SingletonRouter.router?.change) {
      return;
    }

    // @ts-ignore because "change" is private in Next.js
    const originalChangeFunction = SingletonRouter.router.change;
    const originalOnBeforeUnloadFunction = window.onbeforeunload;

    /*
     * Modifying the window.onbeforeunload event stops the browser tab/window from
     * being closed or refreshed. Since it is not possible to alter the close or reload
     * alert message, an empty string is passed to trigger the alert and avoid confusion
     * about the option to modify the message.
     */
    if (shouldPreventLeaving) {
      window.onbeforeunload = () => '';
    } else {
      window.onbeforeunload = originalOnBeforeUnloadFunction;
    }

    /*
     * Overriding the router.change function blocks Next.js route navigations
     * and disables the browser's back and forward buttons. This opens up the
     * possibility to use the window.confirm alert instead.
     */
    if (shouldPreventLeaving) {
      // @ts-ignore because "change" is private in Next.js
      SingletonRouter.router.change = async (...args) => {
        const [historyMethod, , as] = args;
        // @ts-ignore because "state" is private in Next.js
        const currentUrl = SingletonRouter.router?.state.asPath.split('?')[0];
        const changedUrl = as.split('?')[0];
        const hasNavigatedAwayFromPage = currentUrl !== changedUrl;
        const wasBackOrForwardBrowserButtonClicked = historyMethod === 'replaceState';
        let confirmed = false;

        if (hasNavigatedAwayFromPage) {
          confirmed = await confirmationDialog(message);
        }

        if (confirmed) {
          // @ts-ignore because "change" is private in Next.js
          Router.prototype.change.apply(SingletonRouter.router, args);
        } else if (wasBackOrForwardBrowserButtonClicked && hasNavigatedAwayFromPage) {
          /*
           * The URL changes even if the user clicks "false" to navigate away from the page.
           * It is necessary to update it to reflect the current URL.
           */
          // @ts-ignore because "state" is private in Next.js
          await SingletonRouter.router?.push(SingletonRouter.router?.state.asPath);

          /*
           * @todo
           *   I attempted to determine if the user clicked the forward or back button on the browser,
           *   but was unable to find a solution after several hours of effort. As a result, I temporarily
           *   hardcoded it to assume the back button was clicked, since that is the most common scenario.
           *   However, this may cause issues with the URL if the forward button is actually clicked.
           *   I hope that a solution can be found in the future.
           */
          const browserDirection = 'back';

          browserDirection === 'back'
            ? history.go(1) // back button
            : history.go(-1); // forward button
        }
      };
    }

    /*
     * When the component is unmounted, the original change function is assigned back.
     */
    return () => {
      // @ts-ignore because "change" is private in Next.js
      SingletonRouter.router.change = originalChangeFunction;
      window.onbeforeunload = originalOnBeforeUnloadFunction;
    };
  }, [shouldPreventLeaving, message, confirmationDialog]);
};

This seems to break the browser navigation on IOS. It seems like confirm isnt "await'able"? Or maybe ios refuses to show a confirm when using the browser navigation?

EDIT,
Ios DOES ignore confirm, alert and other methods when using the browser navigation. I was able to solve this by making my own confirm modal that wraps a promise and waits for the users confirmation.

Hmm, I also have my own custom modal so maybe that is why I haven't noticed it breaking.

@kirkegaard Can you add a link your modal/promise code via a Gist or Repo? I would like to see how you did it.

I threw this together real quick but something like this :)
https://codesandbox.io/p/sandbox/cocky-northcutt-vbww1k

I dont think its the best approach. It seems kind of hacky and doesnt handle if the user clicks the back button twice.

Are you doing it without a promise? If so, how? If you have a better way please let me know :) My way feels so sketchy!

Hello,
great piece of code!
I have one question: is it possible to perform a custom action instead of showing the alert?

I am trying to use this code to close a modal when back is pressed, instead of navigating back.

If I pass a callback to the hook and call it at line #53, it is not executed but I still get the alert.

Hmm, I also have my own custom modal so maybe that is why I haven't noticed it breaking.

@kirkegaard Can you add a link your modal/promise code via a Gist or Repo? I would like to see how you did it.

Could you show me the example of the custom modal?

Check out this PR/branch to see how I make a custom dialog

codeBelt/warn-unsaved-changes-leaving-web-page-nextjs#3

Check out this PR/branch to see how I make a custom dialog

codeBelt/warn-unsaved-changes-leaving-web-page-nextjs#3

I did myself with promise and resolve using hooks and context. I think yours are similar but using a global store. However there're still two cases not solved properly. I've ported your code to my nextjs 13 page router, and confirmed with your example website too.

• the tab refresh and close still defaults to chrome native dialog, I've also exhausted a ton of time finding alternatives, but not found any.
• For the browser button nav back and forward, I see you push the state, but chrome doesn't respect that, the url doesn't change back to current, if cancelled out.

what about app router in next 13?? i can't use this for app router because router in next13 come from next/navigation