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What are Modules and Components in Angular?
May 9, 2020

Introduction to Angular concepts Part 1

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 are NgModules, which provide a compilation context for components.

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.

Both components and services are simply classes, with decorators that 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.

Modules

Angular NgModules differ from and complement JavaScript (ES2015) modules.

An NgModule declares a compilation context for a set of components that is dedicated to an application domain, a workflow, or a closely related set of capabilities.

An NgModule can associate its components with related code, such as services, to form functional units.

Every Angular app has a root module, conventionally named AppModule, which provides the bootstrap mechanism that launches the application.

An app typically contains many functional modules.

Like JavaScript modules, NgModules can import functionality from other NgModules, and allow their own functionality to be exported and used by other NgModules.

For example, to use the router service in your app, you import the Router NgModule.

Organizing your code into distinct functional modules helps in managing development of complex applications, and in designing for reusability.

In addition, this technique lets you take advantage of lazy-loading—that is, loading modules on demand—to minimize the amount of code that needs to be loaded at startup.

Components

Every Angular application has at least one component, the root component that connects a component hierarchy with the page document object model (DOM).

Each component defines a class that contains application data and logic, and is associated with an HTML template that defines a view to be displayed in a target environment.

The @Component() decorator identifies the class immediately below it as a component, and provides the template and related component-specific metadata.

Decorators are functions that modify JavaScript classes.

Angular defines a number of decorators that attach specific kinds of metadata to classes, so that the system knows what those classes mean and how they should work.

Credit: Angular.io

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