Angular JS 2

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Module

• The module component is a block of code which can be used to perform a single task. 
• You can export the value of something from the code such as a class. 
• The Angular apps are called as modules and build your application using many modules. 
• The basic building block of Angular 2 is a component class which can be exported from a module.

Component 

• is a controller class with a template which deals with a view and logic on the page. 
• Component knows how to render itself and configure dependency injection. 
• You can associate CSS styles using component inline styles, style urls and template inline styles to a component.
• To register component, we use @Component annotation and can be used to break up the application into smaller parts. There will be only one component per DOM element.

Template

• The component's view can be defined by using the template which tells Angular how to display the component.
• To display the value, you can put template expression {{name}} within the interpolation braces.

Metadata

• Metadata is a way of processing the class. 
• E.g. we have one component called MyComponent which will be a class until we tell Angular that it's a component. You can use metadata to the class to tell Angular that MyComponent is a component. 
• The metadata can be attached to TypeScript by using the decorator.

Data Binding

• Data binding is a process of coordinating application data values by declaring bindings between sources and target HTML elements. 
• It combines the template parts with components parts and template HTML is bound with markup to connect both sides. 
• There are four types of data binding:
• Interpolation: It displays the component value within the div tags.
• Property Binding: It passes the property from the parent to property of the child.
• Event Binding: It fires when you click on the components method name.
• Two-way Binding: This form binds property and event by using the ngModel directive in a single notation.

Service

• Services are used for reusable data services to access data (Get Data From API / Databases) to from or share by all components.
• Angular services are injected using Dependency Injection mechanism. (asynchronous) 
• So Component only focus for supporting the view.
• Service includes the value, function or feature which is required by the application. Generally, service is a class which can perform something specific such as logging service, data service, message service, the configuration of application etc. There is nothing much about service in Angular and there is no ServiceBase class, but still services can be treated as fundamental to Angular application.

Directive

• The directive is a class that represents the metadata. There are three types of directives:
• Component Directive: It creates custom controller by using view and controller and used as custom HTML element.
• Decorator Directive: It decorates the elements using additional behavior.
• Template Directive: It converts HTML into a reusable template.

Dependency Injection

• Dependency Injection is a design pattern that passes an object as dependencies in different components across the application. It creates new a instance of class along with its required dependencies.

You must remember the below points while using Dependency Injection:

• The Dependency Injection is stimulated into the framework and can be used everywhere.

• The injector mechanism maintains service instance and can be created using a provider.

• The provider is a way of creating a service.

• You can register the providers along with injectors.