knockout
Knockout makes it easier to create rich, responsive UIs with JavaScript
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I constantly find myself using this idiom in KO-based HTML templates:
<!-- ko if: isEdit -->
<td><input type="text" name="email" data-bind="value: email" /></td>
<!-- /ko -->
<!-- ko ifnot: isEdit -->
<td data-bind="text: email"></td>
<!-- /ko -->
Is there a better/cleaner way to do conditionals in KO, or is there a better approach than just using traditional if-else constructs?
Also, I would just like to point out that some versions of Internet Explorer (IE 8/9) don't parse the above example correctly. Please see this SO question for more information. The quick summary is, don't use comments (virtual bindings) inside table tags to support IE. Use the tbody instead:
<tbody data-bind="if: display"><tr><td>hello</td></tr></tbody>
Source: (StackOverflow)
I've written a few custom bindings using KnockoutJS. I'm still unsure when to use ko.util.unwrapObservable(item) Looking at the code, that call basically checks to see if item is an observable. If it is, return the value(), if it's not, just return the value. Looking at the section on Knockout about creating custom bindings, they have the following syntax:
var value = valueAccessor(), allBindings = allBindingsAccessor();
var valueUnwrapped = ko.utils.unwrapObservable(value);
In this case, they invoke the observable via () but then also call ko.utils.unwrapObservable. I'm just trying to get a handle on when to use one vs. the other or if I should just always follow the above pattern and use both.
Source: (StackOverflow)
I'd like to use a property on my ViewModel to toggle which icon to display without creating a separate computed property of the inverse. Is this possible?
<tbody data-bind="foreach: periods">
<tr>
<td>
<i class="icon-search" data-bind="visible: !charted, click: $parent.pie_it"></i>
<i class="icon-remove" data-bind="visible: charted, click: $parent.pie_it"></i>
</td>
</tr>
</tbody>
My ViewModel has a property periods which is an array of month, like this:
var month = function() {
this.charted = ko.observable(false);
};
Source: (StackOverflow)
I need to have multiple data bindings on one element. For example, I want a href as well as a html data-binding on one a tag. I have tried this,
<a data-bind="html: name"
data-bind="attr: { href: url }"
data-bind="attr: { 'data-prop': xyz }">
</a>
But this doesn't work. It seems knockout only supports binding one data-bind property? How to bind both the href, the inner html, and a custom "data-prop" attribute on one element?
Source: (StackOverflow)
I'm getting this Error:
The JSON request was too large to be deserialized.
Here's a scenario where this occurs. I have a class of country which hold a list of shipping ports of that country
public class Country
{
public int Id { get; set; }
public string Name { get; set; }
public List<Port> Ports { get; set; }
}
I use KnockoutJS on the client side to make a cascading drop downs. So we have an array of two drop downs, where the first one is country, and the second one is ports of that country.
Everything is working fine so far, this my client side script:
var k1 = k1 || {};
$(document).ready(function () {
k1.MarketInfoItem = function (removeable) {
var self = this;
self.CountryOfLoadingId = ko.observable();
self.PortOfLoadingId = ko.observable();
self.CountryOfDestinationId = ko.observable();
self.PortOfDestinationId = ko.observable();
};
k1.viewModel = function () {
var marketInfoItems = ko.observableArray([]),
countries = ko.observableArray([]),
saveMarketInfo = function () {
var jsonData = ko.toJSON(marketInfoItems);
$.ajax({
url: 'SaveMarketInfos',
type: "POST",
data: jsonData,
datatype: "json",
contentType: "application/json charset=utf-8",
success: function (data) {
if (data) {
window.location.href = "Fin";
} else {
alert("Can not save your market information now!");
}
},
error: function (data) { alert("Can not save your contacts now!"); }
});
},
loadData = function () {
$.getJSON('../api/ListService/GetCountriesWithPorts', function (data) {
countries(data);
});
};
return {
MarketInfoItems: marketInfoItems,
Countries: countries,
LoadData: loadData,
SaveMarketInfo: saveMarketInfo,
};
} ();
The problem occurs when a country like China is selected, which has lots of ports. So if you have 3 or 4 times "China" in your array and I want to send it to the server to save. The error occurs.
What should I do to remedy this?
Source: (StackOverflow)
In my view model I have a IsMale value that has the value true or false.
In my UI I wish to bind it to the following radio buttons:
<label>Male
<input type="radio" name="IsMale" value="true" data-bind="checked:IsMale"/>
</label>
<label>Female
<input type="radio" name="IsMale" value="false" data-bind="checked:IsMale"/>
</label>
The problem I think is checked expects a string "true" / "false". So my question is, how can I get this 2-way binding w/ this UI and model?
Source: (StackOverflow)
I would like to build a mobile app, brewed from nothing more but html/css and JavaScript. While I have a decent knowledge of how to build a web app with JavaScript, I thought I might have a look into a framework like jquery-mobile.
At first, I thought jquery-mobile was nothing more then a widget framework which targets mobile browsers. Very similar to jquery-ui but for the mobile world. But I noticed that jquery-mobile is more than that. It comes with a bunch of architecture and let's you create apps with a declarative html syntax. So for the most easy thinkable app, you wouldn't need to write a single line of JavaScript by yourself (which is cool, because we all like to work less, don't we?)
To support the approach of creating apps using a declarative html syntax, I think it's a good take to combine jquery-mobile with knockoutjs. Knockoutjs is a client-side MVVM framework that aims to bring MVVM super powers known from WPF/Silverlight to the JavaScript world.
For me MVVM is a new world. While I have already read a lot about it, I have never actually used it myself before.
So this posting is about how to architecture an app using jquery-mobile and knockoutjs together. My idea was to write down the approach that I came up with after looking at it for several hours, and have some jquery-mobile/knockout yoda to comment it, showing me why it sucks and why I shouldn't do programming in the first place ;-)
The html
jquery-mobile does a good job providing a basic structure model of pages. While I am well aware that I could have my pages to be loaded via ajax afterwards, I just decided to keep all of them in one index.html file. In this basic scenario we are talking about two pages so that it shouldn't be too hard to stay on top of things.
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
<link rel="stylesheet" rel='nofollow' href="libs/jquery-mobile/jquery.mobile-1.0a4.1.css" />
<link rel="stylesheet" rel='nofollow' href="app/base/css/base.css" />
<script src="libs/jquery/jquery-1.5.0.min.js"></script>
<script src="libs/knockout/knockout-1.2.0.js"></script>
<script src="libs/knockout/knockout-bindings-jqm.js" type="text/javascript"></script>
<script src="libs/rx/rx.js" type="text/javascript"></script>
<script src="app/App.js"></script>
<script src="app/App.ViewModels.HomeScreenViewModel.js"></script>
<script src="app/App.MockedStatisticsService.js"></script>
<script src="libs/jquery-mobile/jquery.mobile-1.0a4.1.js"></script>
</head>
<body>
<!-- Start of first page -->
<div data-role="page" id="home">
<div data-role="header">
<h1>Demo App</h1>
</div><!-- /header -->
<div data-role="content">
<div class="ui-grid-a">
<div class="ui-block-a">
<div class="ui-bar" style="height:120px">
<h1>Tours today (please wait 10 seconds to see the effect)</h1>
<p><span data-bind="text: toursTotal"></span> total</p>
<p><span data-bind="text: toursRunning"></span> running</p>
<p><span data-bind="text: toursCompleted"></span> completed</p>
</div>
</div>
</div>
<fieldset class="ui-grid-a">
<div class="ui-block-a"><button data-bind="click: showTourList, jqmButtonEnabled: toursAvailable" data-theme="a">Tour List</button></div>
</fieldset>
</div><!-- /content -->
<div data-role="footer" data-position="fixed">
<h4>by Christoph Burgdorf</h4>
</div><!-- /header -->
</div><!-- /page -->
<!-- tourlist page -->
<div data-role="page" id="tourlist">
<div data-role="header">
<h1>Bar</h1>
</div><!-- /header -->
<div data-role="content">
<p><a rel='nofollow' href="#home">Back to home</a></p>
</div><!-- /content -->
<div data-role="footer" data-position="fixed">
<h4>by Christoph Burgdorf</h4>
</div><!-- /header -->
</div><!-- /page -->
</body>
</html>
The JavaScript
So let's come to the fun part - the JavaScript!
When I started to think about layering the app, I have had several things in mind (e.g. testability, loose coupling). I'm going to show you how I decided to split of my files and comment things like why did I choose one thing over another while I go...
App.js
var App = window.App = {};
App.ViewModels = {};
$(document).bind('mobileinit', function(){
// while app is running use App.Service.mockStatistic({ToursCompleted: 45}); to fake backend data from the console
var service = App.Service = new App.MockedStatisticService();
$('#home').live('pagecreate', function(event, ui){
var viewModel = new App.ViewModels.HomeScreenViewModel(service);
ko.applyBindings(viewModel, this);
viewModel.startServicePolling();
});
});
App.js is the entry point of my app. It creates the App object and provides a namespace for the view models (soon to come). It listenes for the mobileinit event which jquery-mobile provides.
As you can see, I'm creating a instance of some kind of ajax service (which we will look at later) and save it to the variable "service".
I also hook up the pagecreate event for the home page in which I create an instance of the viewModel that gets the service instance passed in. This point is essential to me. If anybody thinks, this should be done differently, please share your thoughts!
The point is, the view model needs to operate on a service (GetTour/, SaveTour etc.). But I don't want the ViewModel to know any more about it. So for example, in our case, I'm just passing in a mocked ajax service because the backend hasn't been developed yet.
Another thing I should mention is that the ViewModel has zero knowledge about the actual view. That's why I'm calling ko.applyBindings(viewModel, this) from within the pagecreate handler. I wanted to keep the view model seperated from the actual view to make it easier to test it.
App.ViewModels.HomeScreenViewModel.js
(function(App){
App.ViewModels.HomeScreenViewModel = function(service){
var self = {}, disposableServicePoller = Rx.Disposable.Empty;
self.toursTotal = ko.observable(0);
self.toursRunning = ko.observable(0);
self.toursCompleted = ko.observable(0);
self.toursAvailable = ko.dependentObservable(function(){ return this.toursTotal() > 0; }, self);
self.showTourList = function(){ $.mobile.changePage('#tourlist', 'pop', false, true); };
self.startServicePolling = function(){
disposableServicePoller = Rx.Observable
.Interval(10000)
.Select(service.getStatistics)
.Switch()
.Subscribe(function(statistics){
self.toursTotal(statistics.ToursTotal);
self.toursRunning(statistics.ToursRunning);
self.toursCompleted(statistics.ToursCompleted);
});
};
self.stopServicePolling = disposableServicePoller.Dispose;
return self;
};
})(App)
While you will find most knockoutjs view model examples using an object literal syntax, I'm using the traditional function syntax with a 'self' helper objects. Basically, it's a matter of taste. But when you want to have one observable property to reference another, you can't write down the object literal in one go which makes it less symmetric. That's one of the reason why I'm choosing a different syntax.
The next reason is the service that I can pass on as a parameter as I mentioned before.
There is one more thing with this view model which I'm not sure if I did choose the right way. I want to poll the ajax service periodically to fetch the results from the server. So, I have choosen to implement startServicePolling/*stopServicePolling* methods to do so. The idea is to start the polling on pageshow, and stop it when the user navigates to different page.
You can ignore the syntax which is used to poll the service. It's RxJS magic. Just be sure I'm polling it and update the observable properties with the returned result as you can see in the Subscribe(function(statistics){..}) part.
App.MockedStatisticsService.js
Ok, there is just one thing left to show you. It's the actual service implementation. I'm not going much into detail here. It's just a mock that returns some numbers when getStatistics is called. There is another method mockStatistics which I use to set new values through the browsers js console while the app is running.
(function(App){
App.MockedStatisticService = function(){
var self = {},
defaultStatistic = {
ToursTotal: 505,
ToursRunning: 110,
ToursCompleted: 115
},
currentStatistic = $.extend({}, defaultStatistic);;
self.mockStatistic = function(statistics){
currentStatistic = $.extend({}, defaultStatistic, statistics);
};
self.getStatistics = function(){
var asyncSubject = new Rx.AsyncSubject();
asyncSubject.OnNext(currentStatistic);
asyncSubject.OnCompleted();
return asyncSubject.AsObservable();
};
return self;
};
})(App)
Ok, I wrote much more as I initially planned to write. My finger hurt, my dogs are asking me to take them for a walk and I feel exhausted. I'm sure there are plenty things missing here and that I put in a bunch of typos and grammer mistakes. Yell at me if something isn't clear and I will update the posting later.
The posting might not seem as an question but actually it is! I would like you to share your thoughts about my approach and if you think it's good or bad or if I'm missing out things.
UPDATE
Due to the major popularity this posting gained and because several people asked me to do so, I have put the code of this example on github:
https://github.com/cburgdorf/stackoverflow-knockout-example
Get it while it's hot!
Source: (StackOverflow)
I would like to push a new item onto an observableArray, but only if the item is not already present. Is there any "find" function or recommended pattern for achieving this in KnockoutJS?
I've noticed that the remove function on an observableArray can receive a function for passing in a condition. I almost want the same functionality, but to only push it if the condition passed in is or is not true.
Source: (StackOverflow)
I'm trying to use KnockoutJS with jQuery UI. I have an input element with a datepicker attached. I'm currently running knockout.debug.1.2.1.js and it seems that the change event is never being caught by Knockout. The element looks like this:
<input type="text" class="date" data-bind="value: RedemptionExpiration"/>
I've even tried changing the valueUpdate event type but to no avail. It seems like Chrome causes a focus event just before it changes the value, but IE doesn't.
Is there some Knockout method that "rebinds all the bindings"? I technically only need the value changed before I send it back to the server. So I could live with that kind of workaround.
I think the problem's the datepicker's fault, but I can't figure out how to fix this.
Any ideas?
Source: (StackOverflow)
In knockout js I see View Models declared as either:
var viewModel = {
firstname: ko.observable("Bob")
};
ko.applyBindings(viewModel );
or:
var viewModel = function() {
this.firstname= ko.observable("Bob");
};
ko.applyBindings(new viewModel ());
What's the difference between the two, if any?
I did find this discussion on the knockoutjs google group but it didn't really give me a satisfactory answer.
I can see a reason if I wanted to initialise the model with some data, for example:
var viewModel = function(person) {
this.firstname= ko.observable(person.firstname);
};
var person = ... ;
ko.applyBindings(new viewModel(person));
But if I'm not doing that does it matter which style I choose?
Source: (StackOverflow)
I'm thinking that my application is getting quite large now, too large to handle each View with a single ViewModel.
So I'm wondering how difficult it would be to create multiple ViewModels and load them all into a single View. With a note that I also need to be able to pass X ViewModel data into Y ViewModel data so the individual ViewModels need to be able to communicate with each other or at least be aware of each other.
For instance I have a <select> drop down, that select drop down has a selected state which allows me to pass the ID of the selected item in the <select> to another Ajax call in a separate ViewModel....
Any points on dealing with numerous ViewModels in a single View appreciated :)
Source: (StackOverflow)
This example of knockout js works so when you edit a field and press TAB, the viewmodel data and hence the text below the fields is updated.
How can I change this code so that the viewmodel data is updated every keypress?
<!doctype html>
<html>
<title>knockout js</title>
<head>
<script type="text/javascript" src="js/knockout-1.1.1.debug.js"></script>
<script type="text/javascript">
window.onload= function() {
var viewModel = {
firstName : ko.observable("Jim"),
lastName : ko.observable("Smith")
};
viewModel.fullName = ko.dependentObservable(function () {
return viewModel.firstName() + " " + viewModel.lastName();
});
ko.applyBindings(viewModel);
}
</script>
</head>
<body>
<p>First name: <input data-bind="value: firstName" /></p>
<p>Last name: <input data-bind="value: lastName" /></p>
<h2>Hello, <span data-bind="text: fullName"> </span>!</h2>
</body>
</html>
Source: (StackOverflow)
Bounty
It's been awhile and I still have a couple outstanding questions. I hope by adding a bounty maybe these questions will get answered.
- How do you use html helpers with knockout.js
Why was document ready needed to make it work(see first edit for more information)
How do I do something like this if I am using the knockout mapping with my view models? As I do not have a function due to the mapping.
function AppViewModel() {
// ... leave firstName, lastName, and fullName unchanged here ...
this.capitalizeLastName = function() {
var currentVal = this.lastName(); // Read the current value
this.lastName(currentVal.toUpperCase()); // Write back a modified value
};
I want to use plugins for instance I want to be able to rollback observables as if a user cancels a request I want to be able to go back to the last value. From my research this seems to be achieved by people making plugins like editables
How do I use something like that if I am using mapping? I really don’t want to go to a method where I have in my view manual mapping were I map each MVC viewMode field to a KO model field as I want as little inline javascript as possible and that just seems like double the work and that’s why I like that mapping.
I am concerned that to make this work easy (by using mapping) I will lose a lot of KO power but on the other hand I am concerned that manual mapping will just be a lot of work and will make my views contain too much information and might become in the future harder to maintain(say if I remove a property in the MVC model I have to move it also in the KO viewmodel)
Original Post
I am using asp.net mvc 3 and I looking into knockout as it looks pretty cool but I am having a hard time figuring out how it works with asp.net mvc especially view models.
For me right now I do something like this
public class CourseVM
{
public int CourseId { get; set; }
[Required(ErrorMessage = "Course name is required")]
[StringLength(40, ErrorMessage = "Course name cannot be this long.")]
public string CourseName{ get; set; }
public List<StudentVm> StudentViewModels { get; set; }
}
I would have a Vm that has some basic properties like CourseName and it will have some simple validation on top of it. The Vm model might contain other view models in it as well if needed.
I would then pass this Vm to the View were I would use html helpers to help me display it to the user.
@Html.TextBoxFor(x => x.CourseName)
I might have some foreach loops or something to get the data out of the collection of Student View Models.
Then when I would submit the form I would use jquery and serialize array and send it to a controller action method that would bind it back to the viewmodel.
With knockout.js it is all different as you now got viewmodels for it and from all the examples I seen they don't use html helpers.
How do you use these 2 features of MVC with knockout.js?
I found this video and it briefly(last few minutes of the video @ 18:48) goes into a way to use viewmodels by basically having an inline script that has the knockout.js viewmodel that gets assigned the values in the ViewModel.
Is this the only way to do it? How about in my example with having a collection of viewmodels in it? Do I have to have a foreach loop or something to extract all the values out and assign it into knockout?
As for html helpers the video says nothing about them.
These are the 2 areas that confuses the heck out of me as not many people seem to talk about it and it leaves me confused of how the initial values and everything is getting to the view when ever example is just some hard-coded value example.
Edit
I am trying what Darin Dimitrov has suggested and this seems to work(I had to make some changes to his code though). Not sure why I had to use document ready but somehow everything was not ready without it.
@model MvcApplication1.Models.Test
@{
Layout = null;
}
<!DOCTYPE html>
<html>
<head>
<title>Index</title>
<script src="../../Scripts/jquery-1.5.1.js" type="text/javascript"></script>
<script src="../../Scripts/knockout-2.1.0.js" type="text/javascript"></script>
<script src="../../Scripts/knockout.mapping-latest.js" type="text/javascript"></script>
<script type="text/javascript">
$(function()
{
var model = @Html.Raw(Json.Encode(Model));
// Activates knockout.js
ko.applyBindings(model);
});
</script>
</head>
<body>
<div>
<p>First name: <strong data-bind="text: FirstName"></strong></p>
<p>Last name: <strong data-bind="text: LastName"></strong></p>
@Model.FirstName , @Model.LastName
</div>
</body>
</html>
I had to wrap it around a jquery document ready to make it work.
I also get this warning. Not sure what it is all about.
Warning 1 Conditional compilation is turned off -> @Html.Raw
So I have a starting point I guess at least will update when I done some more playing around and how this works.
I am trying to go through the interactive tutorials but use the a ViewModel instead.
Not sure how to tackle these parts yet
function AppViewModel() {
this.firstName = ko.observable("Bert");
this.lastName = ko.observable("Bertington");
}
or
function AppViewModel() {
// ... leave firstName, lastName, and fullName unchanged here ...
this.capitalizeLastName = function() {
var currentVal = this.lastName(); // Read the current value
this.lastName(currentVal.toUpperCase()); // Write back a modified value
};
Edit 2
I been able to figure out the first problem. No clue about the second problem. Yet though. Anyone got any ideas?
@model MvcApplication1.Models.Test
@{
Layout = null;
}
<!DOCTYPE html>
<html>
<head>
<title>Index</title>
<script src="../../Scripts/jquery-1.5.1.js" type="text/javascript"></script>
<script src="../../Scripts/knockout-2.1.0.js" type="text/javascript"></script>
<script src="../../Scripts/knockout.mapping-latest.js" type="text/javascript"></script>
<script type="text/javascript">
$(function()
{
var model = @Html.Raw(Json.Encode(Model));
var viewModel = ko.mapping.fromJS(model);
ko.applyBindings(viewModel);
});
</script>
</head>
<body>
<div>
@*grab values from the view model directly*@
<p>First name: <strong data-bind="text: FirstName"></strong></p>
<p>Last name: <strong data-bind="text: LastName"></strong></p>
@*grab values from my second view model that I made*@
<p>SomeOtherValue <strong data-bind="text: Test2.SomeOtherValue"></strong></p>
<p>Another <strong data-bind="text: Test2.Another"></strong></p>
@*allow changes to all the values that should be then sync the above values.*@
<p>First name: <input data-bind="value: FirstName" /></p>
<p>Last name: <input data-bind="value: LastName" /></p>
<p>SomeOtherValue <input data-bind="value: Test2.SomeOtherValue" /></p>
<p>Another <input data-bind="value: Test2.Another" /></p>
@* seeing if I can do it with p tags and see if they all update.*@
<p data-bind="foreach: Test3">
<strong data-bind="text: Test3Value"></strong>
</p>
@*took my 3rd view model that is in a collection and output all values as a textbox*@
<table>
<thead><tr>
<th>Test3</th>
</tr></thead>
<tbody data-bind="foreach: Test3">
<tr>
<td>
<strong data-bind="text: Test3Value"></strong>
<input type="text" data-bind="value: Test3Value"/>
</td>
</tr>
</tbody>
</table>
Controller
public ActionResult Index()
{
Test2 test2 = new Test2
{
Another = "test",
SomeOtherValue = "test2"
};
Test vm = new Test
{
FirstName = "Bob",
LastName = "N/A",
Test2 = test2,
};
for (int i = 0; i < 10; i++)
{
Test3 test3 = new Test3
{
Test3Value = i.ToString()
};
vm.Test3.Add(test3);
}
return View(vm);
}
Source: (StackOverflow)
Note: this is mostly for debugging and understanding KnockoutJS.
Is there a way to explicitly request Knockout to refresh the view from (already bound) view model? I am looking for something like:
ko.refreshView();
I understand that this is not an intended use of Knockout, but I still want to know if there is a such method for debugging and learning purposes.
Source: (StackOverflow)
I keep having trouble with debugging problems in KnockoutJS templates.
Say I want to bind to a property called "items" but in the template I make a typo and bind to the (non existing) property "item".
Using the Chrome debugger only tells me:
"item" is not defined.
Are there tools, techniques or coding styles that help me get more information about the binding problem?
Source: (StackOverflow)