MVVM And Linq In Javascript for .NET Programmers


ANOOP MADHUSUDANAN

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image If you are not using a well structured javascript library like JQuery, and still manage to do web development, you are .. hm.. probably interested in contributing too much to the garbage that is already there in the web (I am being nice here :)).

Anyway, this post is about few more cool Javascript libraries other than JQuery, that may generate a lot of interest for .NET Programmers (I am talking with Vin lately a lot about this). In this post, I’ll cover two nice little JavaScript libraries, that’ll bring Model View View Model and LINQ to JavaScript.

1 – Knockcout.js

Knockcout is a cool Javascript library that’ll bring the MVVM concepts to the Javascript. If you are already familiar with MVVM, you are good to use Knockout once you learn the little syntax differences. Here is a quick example that shows how to bind a text variable and a command.

<div>
    You've clicked <span data-bind="text: numberOfClicks"></span> times
    <button data-bind="click: clickCommand">Click me</button>
</div>
 
<script type="text/javascript">
    var viewModel = {
        numberOfClicks : ko.observable(0), 
        clickCommand : function() {
            var previousCount = this.numberOfClicks();
            this.numberOfClicks(previousCount + 1);
        }
    };
</script>

In the viewModel, we’ve a numberOfClicks variable, and also a clickCommand. You’ll see that we are binding the clickCommand to the button. When ever the button is clicked, the numberOfClicks variable is incremented. If you are wondering why we are using ko.observable to assign value to our numberOfClicks property, it is because

you need to declare your model properties as observables, because these are special JavaScript objects that can notify subscribers about changes, and can automatically detect dependencies.

Also, note that to get/set values to our numberOfClicks property, we are relying on methods (), to ensure cross browser compatibility. For this reason, all observable objects are functions. Also, note the data-bind attribute we use for binding the view model variables to the UI elements. Apart from these little differences, it is pretty easy to sail through knockout, and you can easily master MVVM in Javascript

Knockout is a JavaScript library that helps you to create rich, responsive display and editor user interfaces with a clean underlying data model. Any time you have sections of UI that update dynamically (e.g., changing depending on the user’s actions or when an external data source changes), KO can help you implement it more simply and maintainably.

Have a look at http://knockoutjs.com/

2 – Linq.js

If you love Linq, you’ll love Linq.js – it is an almost complete implementation of Linq for Javascript. You can use Enumerable.From(…) to convert an Array to an enumerable, to query them. Here is a quick example.

var array = [100, 200, 30, 40, 500, 40, 200];
var ex1 = Enumerable.From(array).Distinct().ToArray(); // [100, 200, 30, 40, 500]

Linq.js also has a JQuery extension, which is very handy.

Features include

  • implementation of all .NET 4.0 methods and many extra methods (inspiration from Rx, Achiral, Haskell, Ruby, etc...)
  • complete lazy evaluation
  • full IntelliSense support for VisualStudio
  • two versions - linq.js and jquery.linq.js (jQuery plugin)
  • support Windows Script Host
  • binding for Reactive Extensions for JavaScript(RxJS) and IntelliSense Generator -> see documentation
  • NuGet install support(linq.js, linq.js-jQuery, linq.js-Bindings)

Get it from http://linqjs.codeplex.com/

 

Happy coding, Enjoy.

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