submit during beforeunload, maybe who knows radically another method solution

Question

Reviewed many similar questions on stackoverflow.com (also on other resources), but found no answers. So I simplified and generalized questions. It seems like the obvious solution:

$(document).ready(function() {
    var a = 3;
    var b = 5;

    // no message when pressed submit button
    $('form').submit(function() {
        $(window).off('beforeunload');
    });

    // confirm of the need to save
    $(window).on('beforeunload', function(e) {
        if (a != b)
            if (confirm('You changed data. Save?')) {
                $('form').submit();
                // alert('Your data is saved. (With alert submit() work only in FireFox!?)');
            }
    });
});

But not submit work. If you use the alert(), it works only in FireFox. I would like to correct (possibly without delay) cross-browser solution. Maybe who knows radically another method solution.

P.S. On some originality beforeunload described here in the first part: https://stackoverflow.com/a/6065085/1356425, but this is not the solution obvious functional.

Answer 1

I used synchronous AJAX (JAX) request and run handler for events onUnload or onBeforeUnload once for the respective browser. This solution has a single and almost cross-browser behavior.

Example (on jsfiddle):

$(document).ready(function() {

    var form = $('form');
    var textareas = $('textarea');

    function array_compare(a_0, a_1) {
        if(a_0.length != a_1.length)
            return false;

        for(i = 0; i < a_0.length; i++)
            if(a_0[i] != a_1[i])
                return false;

        return true;
    }

    var flag = false; // flag to control the execution of the unloadHandler() once
    var a_open = []; // array with data before unload

    $('textarea').each(function(index) {
        a_open.push($(this).val());
    });

    function unloadHandler() {
        if (flag)
            return;

        var a_close = []; // array with data during unload
        $('textarea').each(function(index) {
            a_close.push($(this).val());
        });

        if (!array_compare(a_open, a_close)) {
            if (confirm('You changed the data, but not saved them. Save?')) {
                $.ajax({
                    type: 'POST',
                    url: '/echo/json/',
                    async: false,
                    data: form.serialize()/* {
                        json: JSON.stringify({
                            text: 'My test text.'
                        }),
                        delay: 3
                    } */,
                    success: function(data) {
                        if (data) {
                            console.log(data);
                            alert('All data is saved!');
                        }
                    }
                });
            }
        }

        flag = true;
    }

    // For FireFox, Chrome
    $(window).on('beforeunload', function () {
        unloadHandler();
    });

    // For Opera, Konqueror
    $(window).unload(function() {
        unloadHandler();
    });

    // Without message when pressed submit button
    $('form').submit(function() {
        $(window).off('beforeunload');
        $(window).off('unload');
    });

});

Answer 2

Chrome and Firefox blocking submits after the onbeforeunload-event. You have to use

$(window).on('beforeunload', function(e) {
        if (a != b)
            return 'You\'ve changed the data. Leave page anyway?';
        }                
    });

Answer 3

Best way to submit data on unload is to store it in localstorage and send it next time when any other page under same origin is requested.

  function sendBeacon(data) {

    data?dataArr.push(data):'';

    for (var i = 0, len = dataArr.length; i < len; i++) {
        $.getScript(dataArr[i], (function (index) {
            dataArr.splice(index, 1) //Updata dataArray on data submission
        }(i)))
    }
}

$(window).on('beforeunload', function () {
    localStorage.setItem('dataArr', JSON.stringify(dataArr));
})

var dataArr = JSON.parse(localStorage.getItem('dataArr'));

if (!dataArr) {
    dataArr = []; // Create Empty Array
} else {
    sendBeacon(dataArr); //Submit stored data
}