Warn user before leaving web page with unsaved cha

Question

I have some pages with forms in my application.

How can I secure the form in such a way that if someone navigates away or closes the browser tab, they should be prompted to to confirm they really want to leave the form with unsaved data?

Answer 1

You can use serialize() to create a URL encoded text string by serializing form values and check whether the form has changed beforeunload

$(document).ready(function(){
    var form = $('#some-form'),
        original = form.serialize()

    form.submit(function(){
        window.onbeforeunload = null
    })

    window.onbeforeunload = function(){
        if (form.serialize() != original)
            return 'Are you sure you want to leave?'
    }
})

Refer this link https://coderwall.com/p/gny70a/alert-when-leaving-page-with-unsaved-form Written by Vladimir Sidorenko

Answer 2

The solution by Eerik Sven Puudist ...

var isSubmitting = false;

$(document).ready(function () {
    $('form').submit(function(){
        isSubmitting = true
    })

    $('form').data('initial-state', $('form').serialize());

    $(window).on('beforeunload', function() {
        if (!isSubmitting && $('form').serialize() != $('form').data('initial-state')){
            return 'You have unsaved changes which will not be saved.'
        }
    });
})

... spontaneously did the job for me in a complex object-oriented setting without any changes necessary.

The only change I applied was to refer to the concrete form (only one form per file) called "formForm" ('form' -> '#formForm'):

<form ... id="formForm" name="formForm" ...>

Especially well done is the fact that the submit button is being "left alone".

Additionally, it works for me also with the lastest version of Firefox (as of February 7th, 2019).

Answer 3

Short answer:

let pageModified = true

window.addEventListener("beforeunload", 
  () => pageModified ? 'Close page without saving data?' : null
)

Answer 4

Universal solution requiring no configuration that automatically detects all input modification, including contenteditable elements:

"use strict";
(() => {
const modified_inputs = new Set;
const defaultValue = "defaultValue";
// store default values
addEventListener("beforeinput", (evt) => {
    const target = evt.target;
    if (!(defaultValue in target || defaultValue in target.dataset)) {
        target.dataset[defaultValue] = ("" + (target.value || target.textContent)).trim();
    }
});
// detect input modifications
addEventListener("input", (evt) => {
    const target = evt.target;
    let original;
    if (defaultValue in target) {
        original = target[defaultValue];
    } else {
        original = target.dataset[defaultValue];
    }
    if (original !== ("" + (target.value || target.textContent)).trim()) {
        if (!modified_inputs.has(target)) {
            modified_inputs.add(target);
        }
    } else if (modified_inputs.has(target)) {
        modified_inputs.delete(target);
    }
});
addEventListener("beforeunload", (evt) => {
    if (modified_inputs.size) {
        const unsaved_changes_warning = "Changes you made may not be saved.";
        evt.returnValue = unsaved_changes_warning;
        return unsaved_changes_warning;
    }
});
})();