Why mvvm javascript

If left, that could make a pain to maintain such a solution. I think so Invisible to clients but very important to developers. The perfect tech stack, utilities that do all magic to exclude code repeating, long methods names, probably introducing new ways of development, that keep imaginative app developing person to never stop and look up for better libraries for work on the next "impossible" mission.

The set that as minimal and effective, would help to resolve important tasks with less pain, sweat, and tears. Commands are defined in ViewModel. Commands are for anything that is out of fetch and display data.

It is another small sub-layer in separation between Views and ViewModels. If the task is about to update state on the ViewModel, transfer value from input in UI to the backend, update or refresh UI with new data, a command is a good entry point to run such task. Besides exec method, the command can have more methods such as canExecute or inProgress. The second one is to implement an async loading progress overlay on UI.

It will be organized in a way to keep data transfer types as they come from remote service endpoints. With no conversion to types that will be transferred. Just one rule - convenience to receive and transfer data.

Methods that just repeat backend service endpoints. Backend data contact can change with time. In this case, all data will be kept as it is, though, if something will be changed, it would be easy to determine the difference and adjust application.

In the draft version, the backend communication will be simulated by the following " Adapter ":. It doesn't matter how well the Adapter will be programmed. It could be a well-defined solution with generalized fetch and convert methods or it could be just copy-pasted chunks of code that just do data transfer.

Matters just public methods, their signatures, and the results they provide. That smells like the singleton design pattern - current inst. One useful approach is to separate Views from ViewModels.

There, IoC setup could be a good solution. It would allow us to keep all composition between Views and ViewModels in a single place. The IoC setup could grow with the future. Though it would be scary to watch inside of it.

However, it would be just one place, instead of spreading between many smart views. There are more candidates for IoC setup. It is a relation between a TodosModel and Adapter. It is expected to actively communicate between Views, Models, and ViewModels, let's think about a central point. It would be convenient to have one Base class that all those guys will inherit. From there, it would be possible to provide more functionalities to all participants without updating every class.

With that approach, there will be a default public accessor for the internal state of the object. Although event delivering entry point - on and trigger methods.

In the real world, there could be a Base class already defined. That's why I keep on and trigger methods separated from the base implementation. In regards to the base class, it is an adjustable solution. And since it is base class would be great to keep the events listed in a clear way and easily located. An object constructor can serve that purpose. I'm going to initialize all events from the parent class constructor.

Let's not code but just give a thought to the shape of the library, methods and their signatures. To make life easier, the solution will be based on HTML templates with no transformations. Since it is a todo list, the list would have items. Totally, it would require removing, appending items from the todo list. The solution will contain data bindings, which means, HTML wouldn't be redrawn, the list items will be refreshed. All items in the list will just update its data when the list item will change.

Each todo task would have states: active and complete. Last but not the least, listen to DOM events: on , trigger. The TodoModel model will reflect the behavior of the todo list. For that case, there should be a way to keep todo tasks, create new todo from a title, update todo and delete todo.

It will inform participants about the changed state. Keep all fetched data from the backend in the internal state. It will just hold received data. Then data will be passed to ViewModel over events. It should be simple enough to not mess with every item. For the production version, it should deal with paged data, oauth access token, probably partially update state and inform about particular item change.

The tough question is should a model decide about updating its state fetch data when required or allow ViewModel to decide when needs? Let's assume that this. The state of the backend is altered. One item added. And it would be logical to call this.

It would assure that data will be fresh and the model will inform about the state change. It is convenient and it is a restriction. It would be wise to give a second thought. It could lead to unexpected multiple requests to the backend. For instance, in this solution, the updateTodo will be called from two places.

First place - it is when changing the title of the todo task item. This allows us the same level of flexibility as can be found in Backbone. Backbone has a solid routing solution built-in, whilst KnockoutJS offers no routing options out of the box. One can however easily fill this b ehaviour in if needed using Ben Alman's BBQ plugin or a standalone routing system like Miller Medeiros's Crossroads. To conclude, I personally find KnockoutJS more suitable for smaller applications whilst Backbone's feature set really shines when building anything non-trivial.

That said, many developers havevused both frameworks to write applications of varying complexity and I recommend trying out both at a smaller scale before making a decision on which might work best for your project. Skip to content. Sign in Sign up. Instantly share code, notes, and snippets. Created Apr 10, Code Revisions 16 Stars 2 Forks 1. Embed What would you like to do?

Embed Embed this gist in your website. Share Copy sharable link for this gist. Learn more about clone URLs. Download ZIP. Let's now review the three components that compose MVVM. The data bindings in the above markup can be broken down as follows: The input textbox new-todo has a data-binding for the current property, which is where the value of the current item being added is stored.

Our ViewModel shown shortly observes the current property and also has a binding against the add event. When the enter key is pressed, the add event is triggered and our ViewModel can then trim the value of current and add it to the Todo list as needed The input checkbox toggle-all can mark all of the current items as completed if clicked.

If checked, it triggers the allCompleted event, which can be seen in our ViewModel The item li has the class done. When a task is marked as done, the CSS class editing is marked accordingly. An input textbox used for editing mode also holds the value of the Todo item content. The enterKey event will set the editing property to true or false ViewModel The ViewModel can be considered a specialized Controller that acts as a data converter.

Above we are basically providing the methods needed to add, edit or remove items as well as the logic to mark all remaining items as having been completed Note: The only real difference worth noting from previous examples in our ViewModel are observable arrays. Let's now review the advantages and disadvantages of employing the pattern: Advantages MVVM Facilitates easier parallel development of a UI and the building blocks that power it Abstracts the View and thus reduces the quantity of business logic or glue required in the code behind it The ViewModel can be easier to unit test than event-driven code The ViewModel being more Model than View can be tested without concerns of UI automation and interaction Disadvantages For simpler UIs, MVVM can be overkill Whilst data-bindings can be declarative and nice to work with, they can be harder to debug than imperative code where we simply set breakpoints Data-bindings in non-trivial applications can create a lot of book-keeping.

A binding provider is primarily interested in two things: When given a DOM node, does it contain any data-bindings?

If the node passed this first question, what does the binding object look like in the current data context? MVC Vs. MVP Vs. The following notes may be of help here: Both libraries are designed with different goals in mind and its often not as simple as just choosing MVC or MVVM If data-binding and two-way communication are are your main concerns, Knockout is definitely the way to go. This allows us the same level of flexibility as can be found in Backbone Backbone has a solid routing solution built-in, whilst KnockoutJS offers no routing options out of the box.

Sign up for free to join this conversation on GitHub. Already have an account? This abstract approach to their implementation allows them to stay simple, meaning more complex behaviour can be more easily managed on-top as needed. Above we are basically providing the methods needed to add, edit or remove items as well as the logic to mark all remaining items as having been completed Note: The only real difference worth noting from previous examples in our ViewModel are observable arrays.

In KnockoutJS, if we wish to detect and respond to changes on a single object, we would use observables. If however we wish to detect and respond to changes of a collection of things, we can use an observableArray instead.

A simpler example of how to use observables arrays may look as follows:. Note: The complete Knockout. Views and ViewModels communicate using data-bindings and events. Our Views handle their own user-interface events, mapping them to the ViewModel as necessary. Models and attributes on the ViewModel are syncronized and updated via two-way data-binding.

Triggers data-triggers also allow us to further react to changes in the state of our Model attributes. Whilst it may appear the ViewModel is completely responsible for the Model in MVVM, there are some subtleties with this relationship worth noting. The ViewModel can expose a Model or Model attributes for the purposes of data-binding and can also contain interfaces for fetching and manipulating properties exposed in the view. You now hopefully have a better appreciation for what MVVM is and how it works.

KnockoutJS by default has a data-binding provider which searches for any elements with data-bind attributes on them such as in the below example. When the provider locates an element with this attribute, it parses it and turns it into a binding object using the current data context.

This is the way KnockoutJS has always worked, allowing you to declaratively add bindings to elements which KnockoutJS binds to the data at that layer. Once you start building Views that are no longer trivial, you may end up with a large number of elements and attributes whose bindings in markup can become difficult to manage. With custom binding providers however, this is no longer a problem.

We could implement something a little like CSS classes to assign bindings by name to elements. Ryan Niemeyer of knockmeout. Because at one period of time, it can be different by time zone. By storing a number, you can easy compare it, increase, decrease, transfer, At this time, my time zone may be different from yours, but this current time will be store by a number time stamp by stakeoverflow :D.

In your case the model shouldn't hold the already formated string, because it is hart to use it in your program when you need to calculate something for example. If you need more information I would suggestion searching the internet.

Here is one to get you started:. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 5 years, 2 months ago. Active 5 years, 2 months ago. Viewed times.

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