Knockout JS

Javascript   , 14-07-2017

KnockoutJS is basically a library written in JavaScript, based on MVVM pattern that helps developers in building rich and responsive websites. KnockoutJS library provides an easy and clean way to handle complex data-driven interfaces. It is independent of any other framework. This tutorial covers most of the topics required for a basic understanding of KnockoutJS and explains its various functionalities.KO is an abbreviation used for KnockoutJS.Knockout JS is introduced in 2010 by Steve Senderson.

Why KnockoutJS ?

  1. KnockoutJS library provides an easy and clean way to handle complex data-driven interfaces. One can create self-updating UIs for Javascript objects.
  2. It is pure JavaScript Library and works with any web framework. It's not a replacement of Jquery but can work as supplement providing smart features.
  3. KnockoutJS library file is very small & lightweight.
  4. KnockoutJS is independent of any other framework. And is compatible with other client or server side technologies.
  5. Most important of all KnockoutJS is open source and hence free for use.
  6. KnockoutJS is fully documented. The official site has full documentation including API docs, live examples and interactive tutorials.

View

View is nothing but User Interface created using HTML elements and CSS styling.You can bind HTML DOM elements to data model using KnockoutJS. It provides 2 way data binding between View and ViewModel using 'data-bind' concept, which means any updates done in UI are reflected in data model and any changes done in data model are reflected in UI. One can create self-updating UI with help of knockoutJS.

ViewModel

ViewModel is a Javascript object which contains necessary properties and functions to represent data. View and ViewModel are connected together with declarative data-bind concept used in HTML. This makes it easy to change HTML without changing ViewModel. KnockoutJS takes care of automatic data refresh between them through use of Observables.

Synchronization of data is achieved through binding DOM elements to Data Model first using data-bind and then refreshing these 2 components through use of Observables. Dependency tracking is done automatically due to this synchronization of data. No extra coding is required to achieve it. KnockoutJS allows you to create direct connection between your display and underlying data.

You can create your own bindings called as custom bindings for application specific behaviors. This way knockout gives direct control of how you want to transform your data into HTML

Model

Model is domain data on server and it gets manipulated as and when request is sent/received from ViewModel.

The data could be stored in database, cookie or other form of persistent storage. KnockoutJS does not worry about how it is stored. It is up to programmer to communicate between stored data and KnockoutJS.

Most of the times data is saved and loaded via an Ajax call.

Observable Variables

We can declare an observabler variable by using the below format

this.variable=ko.observable(value);

 

Eg:

<input type=”text” data-bind=”value:yourname”>

<script>

Function AppViewmodel(){

this.yourname=ko.observable(“”);

}

Ko.applyBindings(new AppViewmodel())

</script>

Observable Array

Observable declaration takes care of data modifications of a single object. ObservableArray works with the collection of objects. This is a very useful feature when you are dealing with complex applications containing multiple type of values and changing their status frequently based on the user actions.

We can declare an observable array by using the following format

this.arrayname=ko.observableArray();

Disadvantages

  1. Knockoutjs has no routing.
  2. Used to control lower complexity applications.

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