jQuery UI datepicker change event not caught by KnockoutJS

Question

I think that for the jQuery UI datepicker it is preferable to use a custom binding that will read/write with Date objects using the APIs provided by the datepicker.

The binding might look like (from my answer here):

ko.bindingHandlers.datepicker = {
    init: function(element, valueAccessor, allBindingsAccessor) {
        //initialize datepicker with some optional options
        var options = allBindingsAccessor().datepickerOptions || {},
            $el = $(element);

        $el.datepicker(options);

        //handle the field changing by registering datepicker's changeDate event
        ko.utils.registerEventHandler(element, "changeDate", function () {
            var observable = valueAccessor();
            observable($el.datepicker("getDate"));
        });

        //handle disposal (if KO removes by the template binding)
        ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
            $el.datepicker("destroy");
        });

    },
    update: function(element, valueAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor()),
            $el = $(element);

        //handle date data coming via json from Microsoft
        if (String(value).indexOf('/Date(') == 0) {
            value = new Date(parseInt(value.replace(/\/Date\((.*?)\)\//gi, "$1")));
        }

        var current = $el.datepicker("getDate");

        if (value - current !== 0) {
            $el.datepicker("setDate", value);
        }
    }
};

You would use it like:

<input data-bind="datepicker: myDate, datepickerOptions: { minDate: new Date() }" />

Sample in jsFiddle here: http://jsfiddle.net/rniemeyer/NAgNV/

Here is a version of RP Niemeyer's answer that will work with the knockout validation scripts found here: http://github.com/ericmbarnard/Knockout-Validation

ko.bindingHandlers.datepicker = {
    init: function (element, valueAccessor, allBindingsAccessor) {
        //initialize datepicker with some optional options
        var options = allBindingsAccessor().datepickerOptions || {};
        $(element).datepicker(options);

        //handle the field changing
        ko.utils.registerEventHandler(element, "change", function () {
            var observable = valueAccessor();
            observable($(element).val());
            if (observable.isValid()) {
                observable($(element).datepicker("getDate"));

                $(element).blur();
            }
        });

        //handle disposal (if KO removes by the template binding)
        ko.utils.domNodeDisposal.addDisposeCallback(element, function () {
            $(element).datepicker("destroy");
        });

        ko.bindingHandlers.validationCore.init(element, valueAccessor, allBindingsAccessor);

    },
    update: function (element, valueAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor());

        //handle date data coming via json from Microsoft
        if (String(value).indexOf('/Date(') == 0) {
            value = new Date(parseInt(value.replace(/\/Date\((.*?)\)\//gi, "$1")));
        }

        current = $(element).datepicker("getDate");

        if (value - current !== 0) {
            $(element).datepicker("setDate", value);
        }
    }
};

Changes are to the change event handler to pass the entered value and not the date to the validation scripts first, then only setting the date to the observable if it is valid. I also added the validationCore.init that is needed for custom bindings discussed here:

http://github.com/ericmbarnard/Knockout-Validation/issues/69

I also added rpenrose's suggestion for a blur on change to eliminate some pesky datepicker scenarios getting in the way of things.

I've used a different approach. Since knockout.js doesn't seem to fire the event on change, I've forced the datepicker to call change() for its input once closed.

$(".date").datepicker({
    onClose: function() {
        $(this).change(); // Forces re-validation
    }
});

Although all of these answers saved me a lot of work, none of them fully worked for me. After selecting a date, the binded value would not update. I could only get it to update when changing the date value using the keyboard then clicking out of the input box. I fixed this by augmenting RP Niemeyer's code with syb's code to get:

ko.bindingHandlers.datepicker = {
        init: function (element, valueAccessor, allBindingsAccessor) {
            //initialize datepicker with some optional options
            var options = allBindingsAccessor().datepickerOptions || {};

            var funcOnSelectdate = function () {
                var observable = valueAccessor();
                observable($(element).datepicker("getDate"));
            }

            options.onSelect = funcOnSelectdate;

            $(element).datepicker(options);

            //handle the field changing
            ko.utils.registerEventHandler(element, "change", funcOnSelectdate);

            //handle disposal (if KO removes by the template binding)
            ko.utils.domNodeDisposal.addDisposeCallback(element, function () {
                $(element).datepicker("destroy");
            });

        },
        update: function (element, valueAccessor) {

            var value = ko.utils.unwrapObservable(valueAccessor());
            if (typeof(value) === "string") { // JSON string from server
                value = value.split("T")[0]; // Removes time
            }

            var current = $(element).datepicker("getDate");

            if (value - current !== 0) {
                var parsedDate = $.datepicker.parseDate('yy-mm-dd', value);
                $(element).datepicker("setDate", parsedDate);
            }
        }
    };

I suspect putting the observable($(element).datepicker("getDate")); statement in its own function and registering that with options.onSelect did the trick?

Thanks for this article I found it very useful.

If you want the DatePicker to behave exactly like the JQuery UI default behaviour I recommend adding a blur on the element in the change event handler:

i.e.

    //handle the field changing
    ko.utils.registerEventHandler(element, "change", function () {
        var observable = valueAccessor();
        observable($(element).datepicker("getDate"));

        $(element).blur();

    });

I solved this problem by changing the order of my included script files:

<script src="@Url.Content("~/Scripts/jquery-ui-1.10.2.custom.js")"></script>
<script src="@Url.Content("~/Scripts/knockout-2.2.1.js")"></script>