Does knockout.js really employ MVVM pattern?

问题:

I am new to knockout.js. Few moments back I read the headline features of ko. I could not understand is ko really MVVVM? Because all they talk about is data binding and the ease of it. But I am sure MVVM is more than data binding isn't it?

回答1:

Yes, knockout.js does apply the MVVM pattern. It's explained in the documentation:

• A model: your application’s stored data. This data represents objects and operations in your business domain (e.g., bank accounts that can perform money transfers) and is independent of any UI. When using KO, you will usually make Ajax calls to some server-side code to read and write this stored model data.

• A view model: a pure-code representation of the data and operations on a UI. For example, if you’re implementing a list editor, your view model would be an object holding a list of items, and exposing methods to add and remove items.

  Note that this is not the UI itself: it doesn’t have any concept of buttons or display styles. It’s not the persisted data model either - it holds the unsaved data the user is working with. When using KO, your view models are pure JavaScript objects that hold no knowledge of HTML. Keeping the view model abstract in this way lets it stay simple, so you can manage more sophisticated behaviors without getting lost.

• A view: a visible, interactive UI representing the state of the view model. It displays information from the view model, sends commands to the view model (e.g., when the user clicks buttons), and updates whenever the state of the view model changes.

  When using KO, your view is simply your HTML document with declarative bindings to link it to the view model. Alternatively, you can use templates that generate HTML using data from your view model.

回答2:

In addition to the answer already provided, there are a few things to keep in mind -

MVVM

Knockout is MVVM because it supports a good separation of concerns. Unlike other JavaScript libraries, such as jQuery, it's goal is to not pollute the view with that which does not concern it.

The view model's purpose is important to understand. It does not attempt to manipulate the DOM because only logic required to serve up data to the view is placed inside of it.

The view's purpose is only to present (render) the data. No logic, validation, or other logic code goes here.

The model is the only place where Knockout can get a bit tricky. It is generally a good accepted practice to place a separate model in your project for Knockout to use, but many developers have found the ease of mixing the model into the view model. The reason for this is obvious (some models are very basic) but again this is only out of ease of implementation.

MVC vs MV*

Surely there are other answers on SO.com that attempt to answer what is MV*, but I wanted to throw my $0.02 in here - Other libraries or frameworks speak to the fact that they are MVC or MVP or MV(whatever) based but Knockout is the only one that I have found that practices what it preaches in this regard. If you have the time and desire look at the structure of other frameworks such as Angular or Ember and you will see there is a blurred line that exists, and more or less they are simply using an MVVM based pattern but calling it something different.

回答3:

Well I guess it can, however I am working on a project where all styling and UI layout manipulation is done in the knockout js ViewModel file, which is not good practice.