Angular 2 gets rid of controllers

In my previous post I talked about the problems of controllers (both at the back-end and the front-end). The issue is that controllers are too general and tend to become full with mixed logic, especially if the page they control has many UI pieces. So instead of having one controller per page, we can have one controller per component and hence decrease the coupling in one’s code.

Some JavaScript libraries, f.x. React, are designed with the component in the center. In Angular 1.x we have the concepts of a controller and a directive. One can attach a controller to any part of the page or when using a router, a controller is automatically assigned to the view. You can easily remove all usages of controllers on your page simply by moving the code into an appropriate directive. Do not forget that you can also rely on the different types of services in Angular for custom logic.

In Angular 2 the notion of controller is completely removed. You should work with directives only and you can actually choose what kind of a directive you want to use for the specific case:

  • Component directives provide a “static” template with some logic behind. It is the same as a directive with a template and an isolated scope in Angular 1.x
  • Template directives work with a user-defined template. It is similar to a directive with transclude in Angular 1.x
  • Decorator directives add extra functionality to an existing DOM element (see Decorator pattern). It is the same as a directive with no translude, no own scope and no template in Angular 1.x

If you think you will miss the mapping to a controller from the router in Angular 2, you can actually do a mapping to a ComponentDirective instead, but I would still opt for slicing your views into smaller components.

From MVC towards components

The nature of HTTP is to provide resources where each resource is identified by a unique URL. A resource can be any kind of file: image, text file, font. Initially web sites used to deliver static HTML pages, which were pretty much limited in terms of content. CGI and server-side scripting languages like PHP, ASP(.NET), and JSP changed this by generating dynamic HTML on the server and sending it back to the client. This allowed the page content to be “configured” by the browser, f.x. using query string. This traditional web architecture is denoted on the diagram below.

Traditional web architecture

It all worked fine until the Web became more complex and developers started to put more and more logic on the server. We ended up having to make requests like /index.php?module=employees&id=5 (especially with some CMS systems). This architecture tended eventually to cause many problems, from search-engine optimization to code maintenance. Continue Reading…

ES6 generators to the rescue

Arrays are one of the simplest data structures which allow access to a list of elements. JavaScript (and most programming languages) has the notion of array. However one of the problems related to arrays is they are constrained by their size, i.e. an array has a limited number of elements. Furthermore, when applying functions to arrays, one passes the whole data structure at once. Let’s take a look at the following example. The map function is applied to the whole array and the result is calculated right away.

Note, the lambda expression is part of ES6

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Getting declarative with Polymer

Polymer is Google’s implementation of WebComponents for today’s browser. If you are not familiar with it, check out this nice tutorial by Pankaj Parashar. The main idea behind WebComponents is that we should be able to create our own web components (hence the name). A web component is just a custom HTML element with some styles and behavior attached to it. An example can be the following:

Polymer provides two sets of components one can use directly or build on:

  • Core – basic elements, both visual and non-visual, that can help one built layouts, scaffolding, and user interaction
  • Paper – these elements implement the material design philosophy of Google

Continue Reading…