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|STDAFX LINUX||Minimize intermodule and interlayer coupling. A component exists primarily for the purpose of supplying UI output or UI interaction. Handling errors is just as simple. Leaving off the selector is probably a code smell. There can be more than one view listening to a single model.|
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Related videosSeparation of concerns RANT - MPJ's Musings - FunFunFunction #47
Krasimir is a bloggerwho writes and speaks. He loves open source and codes awesome stuff. Follow KrasimirTsonev. Years ago when Facebook announced their JSX syntax we had a wave of comments how this was against some of the well established good practices. The main point of most people was that it violates the separation of concerns. In this article we will see how React and its ecosystem has quite good separation of concerns.
Let's take the following example:. This is the pain point. The place where we are mixing CSS and markup or we may say mixing styling and structure. To solve the issue let's keep UserCard still responsible for the structure, but extract the styling out into dedicated components Card and Avatar:.
Very often we write logic inside our React components which is more then clicking a button and showing a message. The snippet below demonstrates a component that fetches data from a fake API and renders users on the screen. Quite a lot of things are happening isn't it.
It contains data fetching and data representation. The very first thing that we notice is that the constructor and componentDidMount method are just copy-pasted from the App component. Having FetchUsers we may transform our App into a stateless component:. At this point our markup is separated from the logic. We still operate with the same data and as a bonus we sulejman velicanstveni 1 sezona this reusable FetchUsers component that may be dropped anywhere.
My opinion is that React is one level up over the HTML because it allows us to group complex markup into a single component. We still keep them together but now they are easy to move around. Perhaps, there are places where we write some logic directly into the markup like so:. In such cases I again recommend to use composition and remove any app logic concerns out of the presentation.
React and separation of concerns
Separation of concerns is the idea that each module or layer in an application should only be responsible for one thing and should not contain code that deals with other things. Separating concerns reduces code complexity by breaking a large application down into many smaller units of encapsulated functionality.
For example, n-tier architecture and MVC architectures are the result of separating concerns across the entire application, rather than at the individual module level. The goal of MVC and related patterns is to separate data management from presentation.
Separation of concerns can be expressed as functions, modules, controls, widgets, layers, tiers, services, and so on. The various units of concern vary from one app to the next, and each different app may use a different combination. Functions and modules have already been discussed. A control is a reusable GUI input that enables user interaction with your application. For example, combo boxes, calendar inputs, sliders, buttons, switches, and knobs are all controls.
A widget is a small application which is intended to be embedded in other applications. For example, WordPress allows developers to offer embeddable units of functionality to blog owners through its plug-in ecosystem. There are many widgets to manage calendars, comments, maps, and all sorts of services from third-party providers. The word widget is historically used to mean the same thing as controls.
Libraries roughly fall into two categories: Minimal libraries generally provide a handful of objects and methods which make it easier to build well organized applications. Perhaps the most famous example is Backbone. That may sound like a lot, until you compare it to something like the Dojo framework, which is something like a library of libraries.
However, there is some security in using a well-tested library like jQuery because it is used and improved by thousands of other smart developers. Everybody makes mistakes. Be prepared to debug them as you work with them. Please contribute fixes back to the author if you find and fix a bug. I see no good reason to reassemble that feature set from microlibraries every time you start a new project.
Aura is a good example of an open-source implementation with a fairly narrow focus on module management—with one clear difference: Aura has a strong focus on UI components, which are modules that have UI elements that need to be rendered to the screen.
A generic module could perform any type of service and may or may not need a dedicated space to render. A component exists primarily for the purpose of supplying UI output or UI interaction.
For the sake of clarity and simplicity in the following examples, I wrote a simple module management solution called Tinyapp.
There are a couple of ways you could source the environment from the server side: The pageData object is intended to register bootstrapped data with the app at page-load time.
Each item you add to it compounds the possibility that something in the queue will fail, which might significantly delay or block the render of your application. This contrived example should really be simplified even further. If you need to fetch some data asynchronously before you render your module, Tinyapp helps speed things up by launching your asynchronous calls as early as possible. Module initialization is broken into two phases: Imagine you want to asynchronously fetch some data while the page is still loading so that you can begin to render it as early as possible.
This can speed up your perceived page-load times. The solution is to kick off the asynchronous fetch at load time so that it begins the download as early as possible: This will reduce the number of page requests that must be handled at page-load time eliminating the latency hit and hopefully also improve the perceived performance of your app.
Tinyapp allows you to hook into those page-load phases individually so you can optimize page-load times and manage render dependencies without worrying about asynchronous timing issues. You can specify load and render callbacks by passing them into a registration method:. Any promise returned by load is resolved. For example, if you return a jQuery Ajax promise from your load function, it will wait until the Ajax fetch is complete. All jQuery Ajax calls return compatible promises. All beforeRender callbacks have fired see Getting started.
Registration is optional. Time for an example. Imagine you have a widget that displays tour dates for bands. Try not to do anything blocking in your load function. Events are a method of communicating between different application modules or components in order to achieve loose coupling, asynchronous communication, interprocess communication, or any combination of the above. For example, the browser environment is event driven. It presents DOM elements to users buttons and form inputs, for exampleand then responds to user input by firing events for the application to listen for and handle.
This section covers defining and using your own custom events, independent of the DOM. Other modules can listen for the events they care about and decide what to do next on their own.
In situations where there are potentially many objects listening, that strategy requires too much boilerplate code to be maintainable. Another problem you might encounter is that listeners must be tightly coupled to emitters, which partially defeats the purpose of using events in the first place.
An aggregator eliminates the need for specialized mediators to keep an emitter and listener decoupled. Again, with Backbone and Underscore, that might look something like this:. Event aggregators can be enormously useful. Because neither emitter nor subscriber need know about the other, aggregators enable very loose coupling between modules.
Each only needs a reference to the aggregator. In this case, the emitter and the listener only need to know about app.
A message queue is a type of event mediator that records every message it hears in a queue or stack for later processing. There is often a need for separate modules or processes to collaborate in order to process input.