What is Knockout ?

What is Knockout ?

Knockout is a JavaScript Library Which helps the creation of rich, desktop-like web UIs.It simplifies user interactions and makes interfaces fully responsive to any data source changes.Knockout provides a simple two-way binding mechanism to link a data model to an UI,Thus making synchronization between them a breeze.You can read Original Article about this on My Blog Here.

What are the Key Concepts of Knockout ?

1. Declarative Bindings

• These allow you to connect parts of your UI to your data model in a simple and convenient way
• With declarative bindings even if you change the DOM all bound pieces stay connected
• You can bind data to a DOM by simply including a data-bind attribute to any DOM element

2. Automatic UI Refresh

3. Dependency Tracking

• Every time when your model data has changed all parts associated with it automatically being updated
• No need to worry about adding event handlers and listeners
• All that extra work is performed internally by Knockout and observables,
• Which notify listeners when underlying values have changed

4. Templating

• when your application becomes more complex and you need a way to display a rich structure of view model data,thus keeping your code simple
• Knockout has a native, built-in template engine which you can use right away
• But if you want, a third-party template engine, like jquery.tmpl or Underscore, also can be used

More Features of Knockout

How to Download Knockout ?

• You can Download knockout Here

Step 1

Step 2

Step 3

How to work with Knockout ?

1. You have to add a reference to the "knockout-2.2.0.js" File which you downloaded
2. Then You have to add Reference to above file inside your master file

   i.e. Inside \Views\Shared\_Layout.cshtml

   <script src="@Url.Content("~/Scripts/knockout-2.2.0.js")" type="text/javascript"></script>

   That's it.Your done.

Let's try with some basic capabilities of Knockout

ASP.Net MVC 3 and Visual Studio 2010 has been used. 

CASE 1 : How to use bindings in the View (Static Data) ?  

• For that you can use data-bind attributes

View's Code

?<!-- This is a View - HTML markup that defines the appearance of your UI -->
<p>First name: <strong data-bind="text: firstName"></strong></p>
<p>Last name: <strong data-bind="text: lastName"></strong></p>

Javascript Code

<script type="text/javascript">    //This is a simple Viewmodel
    //JavaScript that defines the data and behavior of your UI
    functionAppViewModel() {
        this.firstName = "Sampath";
        this.lastName = "Lokuge";
    }
    //Activates knockout.js
    ko.applyBindings(newAppViewModel());
</script>

Output

CASE 2 : How to Make the data Editable (Dynamic Data) ? 

• That's why Knockout has a concept of observables
• These are properties that automatically will issue notifications whenever their value changes

i.e.

• Not only that the underlying ViewModel data is being updated when you edit ,
• But that all associated UI is updating in Sync with it too

View's Code

<!-- This is a View - HTML markup that defines the appearance of your UI -->
<p>First name: <strong data-bind="text: firstName"></strong></p>
<p>Last name: <strong data-bind="text: lastName"></strong></p>
<p>First name:<input data-bind="value: firstName" /></p>
<p>Last name:<input data-bind="value: lastName" /></p>

Javascript Code

<script type="text/javascript">
    //This is a simple Viewmodel
    //JavaScript that defines the data and behavior of your UI
    functionAppViewModel() {
        this.firstName = ko.observable();
        this.lastName = ko.observable();
    }
    //Activates knockout.js
    ko.applyBindings(newAppViewModel());
</script>

Output

CASE 3 : How to Define Computed Values ?

• To handle this, Knockout has a concept of Computed Properties
• These are observable (i.e., they notify on change)
• And they are computed based on the values of other observables

View's Code

<!-- This is a View - HTML markup that defines the appearance of your UI -->
<p>First name: <strong data-bind="text: firstName"></strong></p>
<p>Last name: <strong data-bind="text: lastName"></strong></p>
<p>First name:<input data-bind="value: firstName" /></p>
<p>Last name:<input data-bind="value: lastName" /></p>
<p>Full name: <strong data-bind="text: fullName"></strong></p>

Javascript Code

Note: In order to simplify things you can create a variable self (i.e. var self = this;)

<script type="text/javascript">
    //This is a simple Viewmodel
    //JavaScript that defines the data and behavior of your UI
    functionAppViewModel() {
        varself = this;
        self.firstName = ko.observable();
        self.lastName = ko.observable();
        self.fullName = ko.computed(function () {
            returnself.firstName() + " " + self.lastName();
        });
    }
    //Activates knockout.js
    ko.applyBindings(newAppViewModel());
</script>

Output

CASE 4 : How to add UPPER-CASE behavior ?

• Need to add a capitalizeLastName function to the viewmodel
• To Read or Write an observable's value, you have to call it as a function

View's Code

<!-- This is a View - HTML markup that defines the appearance of your UI -->
<p>First name: <strong data-bind="text: firstName"></strong></p>
<p>Last name: <strong data-bind="text: lastName"></strong></p>
<p>First name:<input data-bind="value: firstName" /></p>
<p>Last name:<input data-bind="value: lastName" /></p>
<p>Full name: <strong data-bind="text: fullName"></strong></p>
<button data-bind="click: capitalizeLastName"> Go CAPS </button>

Javascript Code

<script type="text/javascript">
   //This is a simple Viewmodel
   //JavaScript that defines the data and behavior of your UI
   functionAppViewModel() {
        varself = this;
        self.firstName = ko.observable();
        self.lastName = ko.observable();
        self.fullName = ko.computed(function () {
           returnself.firstName() + " " + self.lastName();
        });
        self.capitalizeLastName = function () {
            varcurrentVal = self.lastName();//Read the current value
            self.lastName(currentVal.toUpperCase());//Write back a modified value
        };
    }    //Activates knockout.js
    ko.applyBindings(newAppViewModel());
</script>

Output

Small discussion about Knockout on stackoverflow, Which I have involved

• Difference between knockout and .NET View Models ?

Conclusion

• This is a very basic example, but it illustrates some of the key points of Knockout
• You've got a clean, object-oriented representation of your UI's data and behaviors (your viewmodel)
• Separately, you've got a declarative representation of how it should be displayed visibly (your view)
• You can implement arbitrarily sophisticated behaviors just by updating the viewmodel object
• You don't have to worry about which DOM elements need to be changed, added or removed,
• The framework can take care of synchronizing things for you

I hope this helps you. Comments and feedback greatly appreciated.

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