Using Knockout.js how do bind a Date property to a HTML5 date picker?

Question

(this only works in Chrome at the moment as most browsers don't yet implement date picker for input type="date")

In the following example MyDate starts out as a Date object with the current date, but this isn't picked up by the date input (which expects its format to be a string in format YYYY/MM/DD).

Once you've picked a date in the picker then MyDate becomes a string in format above.

How can you bind this so MyDate stays a javascript Date and is interpreted by the input control correctly?

See See http://jsfiddle.net/LLkC4/3/ :-

<input data-bind="value : MyDate" type="date">
<hr>   
<span data-bind="html: log" />

<script>
var viewModel = {    
    MyDate : ko.observable(new Date()),
    log : ko.observable(""),
    logDate : function () { 
            this.log(this.log() + this.MyDate() + " : " +
                     typeof(this.MyDate()) + "<br>");
                     }
};

viewModel.MyDate.subscribe(function (date) {    
    viewModel.logDate();    
});

ko.applyBindings(viewModel);

viewModel.logDate()
</script>

Answer 1

While @amakhrov answer will work (and would be even better if used writeable computed observable like sujested by @Stijn) I decided to do this using Custom Bindings.

The main advantage of doing this is reusability - I just have to use data-bind="datePicker : MyDate" whereever I want to tie this in. I can also modify other properties of the input element so this could be really useful if binding to complex jQuery (and other) controls.

(Read here for more pro/cons about the 3 choices to do this sort of thing)

HTML

<input data-bind="datePicker : MyDate" type="date">

JS

ko.bindingHandlers.datePicker = {
    init: function (element, valueAccessor, allBindingsAccessor, viewModel) {                    
        // Register change callbacks to update the model
        // if the control changes.       
        ko.utils.registerEventHandler(element, "change", function () {            
            var value = valueAccessor();
            value(new Date(element.value));            
        });
    },
    // Update the control whenever the view model changes
    update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
        var value =  valueAccessor();        
        element.value = value().toISOString();
    }
};

var viewModel = {    
    MyDate : ko.observable(new Date())
};     

ko.applyBindings(viewModel);

See http://jsfiddle.net/LLkC4/5/

Answer 2

You can use the computed vartiable for the date object in your model:

In html:

<input data-bind="value : rawDate" type="date">

In code:

var currentDate = (new Date()).toISOString().split('T')[0];

// this is used instead of MyDate in the data binding
rawDate : ko.observable(currentDate),

...
// and then set up the dependent variable
viewModel.MyDate = ko.computed(function () {
    var val = this.rawDate();
    if (typeof val === 'string') val = new Date(val);

    return val;
}, viewModel)

Please see the demo: http://jsfiddle.net/gcAXB/1/

Answer 3

Here's a solution that is working for me with the latest knockoutjs, based off of the link below and modified to have a custom init function to handle updating ko.computed properties as your date value changes.

Note that utils.formatDate is just a utility function to format the date in whatever string you want, so just replace that with your own date formatting code, whether you use momentjs or something else.

ko.bindingHandlers.date = {
    init: function (element, valueAccessor, allBindingsAccessor, viewModel) {    
        ko.utils.registerEventHandler(element, 'change', function () {
            var value = valueAccessor();

            if (element.value !== null && element.value !== undefined && element.value.length > 0) {
                value(element.value);
            }
            else {
                value('');
            }
        });
    },
    update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
        var value = valueAccessor();
        var valueUnwrapped = ko.utils.unwrapObservable(value);

        var output = '';
        if (valueUnwrapped !== null && valueUnwrapped !== undefined && valueUnwrapped.length > 0) {
            output = utils.formatDate(valueUnwrapped);
        }

        if ($(element).is('input') === true) {
            $(element).val(output);
        } else {
            $(element).text(output);
        }
    }
};

    <div>
        <label>Date of Birth:</label>
        <input type="text" data-bind="date: dateOfBirth, format: 'DD MMM YYYY'" />
    </div>

BINDING AND FORMATTING DATES USING KNOCKOUT AND MOMENT JS

Answer 4

These days is so much easier with Moment.js

this.sessionDate = ko.observable(moment().format('YYYY-MM-DD'));
this.getFormattedDate = () => { return moment(this.sessionDate()'YYYY-MM-DD').format('MM/DD/YYYY') }; // Note this is ES2015 syntax

In your html you can bind it with

<input class="form-control" name="date" type="date" id="date" data-bind="value: sessionDate">

And display it formatted as

<p data-bind="text : getFormattedDate()">Loading Date</p>

No need to create custom bindings, and you can use a shim for older browsers.

Answer 5

The same as this custom binding, but using momentJS:

ko.bindingHandlers.datePicker = {
    init: function (element, valueAccessor, allBindingsAccessor, viewModel) {
        // Register change callbacks to update the model
        // if the control changes.
        ko.utils.registerEventHandler(element, "change", function () {
            var value = valueAccessor();
            value(moment(element.value).format());
        });
    },
    // Update the control whenever the view model changes
    update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
        var value =  valueAccessor();
        element.value = moment(value()).format("YYYY-MM-DD");
    }
};

Answer 6

Based off of Ryan's answer above, this works a little nicer with newer ko/chrome widgets. It also strips the time part of the date.

ko.bindingHandlers.datePicker = {
    init: function (element, valueAccessor, allBindingsAccessor, viewModel) {
        // Register change callbacks to update the model
        // if the control changes.
        ko.utils.registerEventHandler(element, "change", function () {
            var value = valueAccessor();
            var target_date = element.valueAsDate;
            var truncated = new Date(target_date.getFullYear(), target_date.getMonth(), target_date.getDate());
            value(truncated);
        });
    },
    // Update the control whenever the view model changes
    update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
        var value =  valueAccessor();
        var unwrapped = ko.utils.unwrapObservable(value());
        if(unwrapped === undefined || unwrapped === null) {
            element.value = '';
        } else {
            element.valueAsDate = unwrapped;
        }
    }
};

Answer 7

From HTML 5 - Input type date formatting on iOS

There are two formats at play:

• displayed format
• internal format exposed to JavaScript and sent to the server

You cannot change the display format. It's up to the browser to decide how the date is presented to the user (in practice it's determined by system's locale).

You cannot change the internal format either. It's always ISO8601, regardless of browser/locale.

You'll have to pre-populate it with that specific format, and you can add a computed observable to parse it into a Date object, so you can read it at other places in your application.

If you also want to write to it from JS, you could set up a writeable computed observable and parse the input to see if it's a string from the input field, or a Date object from your JS.

Answer 8

This worked for me

ko.bindingHandlers.momentDate = {
_parseDateTime: function (element, valueAccessor) {
    var value = valueAccessor();
    var valueUnwrapped = ko.utils.unwrapObservable(value);
    var datetime = moment(valueUnwrapped);
    var date = moment($(element).val(), 'YYYY-MM-DD');
    datetime = datetime.set({
        'year': date.get('year'),
        'month': date.get('month'),
        'date': date.get('date')
    });
    value(datetime.toDate());
},
init: function (element, valueAccessor) {
    function bind() {
        ko.bindingHandlers.momentDate._parseDateTime(element, valueAccessor);
    }
    $(element).change(bind).blur(bind);
},
update: function (element, valueAccessor) {
    var value = valueAccessor();
    var valueUnwrapped = ko.utils.unwrapObservable(value);
    var date = moment(valueUnwrapped);
    $(element).val(date.format('YYYY-MM-DD'));
}

};

<input type="date" data-bind="momentDate: $data.Date" class="form-control"/>

Answer 9

This is probably late but it might help someone out there. I'm using Luxon's DateTime object to easily manage dates and timezones in my application. This works with DateTime objects:

ko.bindingHandlers.dateTime = {
  // Register change callbacks to update the model if the control changes.
  init: function (element, valueAccessor, allBindingsAccessor, viewModel) {
    ko.utils.registerEventHandler(element, 'change', function () {
      const value = valueAccessor()
      const datetime = DateTime.fromFormat(element.value, 'yyyy-MM-dd')
      value(datetime)
    })
  },
  // Update the control whenever the view model changes
  update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
    const value = valueAccessor()
    element.value = ko.unwrap(value).toFormat('yyyy-MM-dd')
  }
}

Usage:

// viewmodel
const today = DateTime.fromFormat(DateTime.now().toFormat('yyyy-MM-dd'), 'yyyy-MM-dd')
this.date = ko.observable(today)

// template
<input type="date" data-bind="dateTime: date">