Basic Intro to Angular Architecture

Angular is a platform and framework for building single-page client applications using HTML and TypeScript. Angular is written in TypeScript. It implements core and optional functionality as a set of TypeScript libraries that you import into your apps.

The architecture of an Angular application relies on certain fundamental concepts. The basic building blocks of the Angular framework are Angular components that are organized into NgModules. NgModules collect related code into functional sets; an Angular app is defined by a set of NgModules. An app always has at least a root module that enables bootstrapping, and typically has many more feature modules.

Components define views, which are sets of screen elements that Angular can choose among and modify according to your program logic and data. Components use services, which provide specific functionality not directly related to views. Service providers can be injected into components as dependencies, making your code modular, reusable, and efficient.

Modules, components and services are classes that use decorators. These decorators mark their type and provide metadata that tells Angular how to use them.

The metadata for a component class associates it with a template that defines a view. A template combines ordinary HTML with Angular directives and binding markup that allow Angular to modify the HTML before rendering it for display. The metadata for a service class provides the information Angular needs to make it available to components through dependency injection (DI).

An app’s components typically define many views, arranged hierarchically. Angular provides the Router service to help you define navigation paths among views. The router provides sophisticated in-browser navigational capabilities.

Angular apps are modular and Angular has its own modularity system called NgModules. NgModules are containers for a cohesive block of code dedicated to an application domain, a workflow, or a closely related set of capabilities. They can contain components, service providers, and other code files whose scope is defined by the containing NgModule. They can import functionality that is exported from other NgModules, and export selected functionality for use by other NgModules.

Every Angular app has at least one NgModule class, the root module, which is conventionally named AppModule and resides in a file named app.module.ts. You launch your app by bootstrapping the root NgModule.

While a small application might have only one NgModule, most apps have many more feature modules. The root NgModule for an app is so named because it can include child NgModules in a hierarchy of any depth.

An NgModule is defined by a class decorated with @NgModule(). The @NgModule() decorator is a function that takes a single metadata object, whose properties describe the module. The most important properties are as follows…

• declarations: The components, directives, and pipes that belong to this NgModule.
• exports: The subset of declarations that should be visible and usable in the component templates of other NgModules.
• imports: Other modules whose exported classes are needed by component templates declared in this NgModule.
• providers: Creators of services that this NgModule contributes to the global collection of services; they become accessible in all parts of the app. (You can also specify providers at the component level.)
• bootstrap: The main application view, called the root component, which hosts all other app views. Only the root NgModule should set the bootstrap property.

A component controls a patch of screen called a view. You define a component’s application logic — what it does to support the view — inside a class. The class interacts with the view through an API of properties and methods.

The @Component decorator identifies the class immediately below it as a component class, and specifies its metadata. The metadata for a component tells Angular where to get the major building blocks that it needs to create and present the component and its view. In particular, it associates a template with the component, either directly with inline code, or by reference. Together, the component and its template describe a view.

In addition to containing or pointing to the template, the @Component metadata configures, for example, how the component can be referenced in HTML and what services it requires.

You define a component’s view with its companion template. A template is a form of HTML that tells Angular how to render the component.

Views are typically arranged hierarchically, allowing you to modify or show and hide entire UI sections or pages as a unit. The template immediately associated with a component defines that component’s host view. The component can also define a view hierarchy, which contains embedded views, hosted by other components.

A view hierarchy can include views from components in the same NgModule, but it also can (and often does) include views from components that are defined in different NgModules.

A template looks like regular HTML, except that it also contains Angular template syntax, which alters the HTML based on your app’s logic and the state of app and DOM data. Your template can use data binding to coordinate the app and DOM data, pipes to transform data before it is displayed, and directives to apply app logic to what gets displayed.

Visiting the Angular Docs is a great way to start learning more about this framework.