udemy.angular/docs/thebasic.md

# The Basic

Angular serves the **index.html** in the `src` directory and loads the components from the `src/app` directory.

The scafolding creates a root-component which is loaded into the index.html on the `<app-root></app-root>`-Tag.

In the `@Component` we find a `selector` with the value of `<app-root></app-root>`. With this selector, Angular is able to replace in the index.thml on the `<app-root></app-root>`-Tag with the content in the app.component.html.

When the app is builded, the angular cli will inject at the bottom a bundle of *.js files which is needet to run the app.

`main.ts` is the file which will be executet at the beginning.


<img src="../img/ngmodule.png" alt="ngmodule" width="800"/><br>
<img src="../img/component.png" alt="component" width="800"/>


Angular's main ideas is to build components to build an app. Each Component has it's own template (html), maybe it's own style (CSS) and more important it's own business logic.
Components can be reused in multiple parts or the application.

## Component

The `app.component` is a special component. It serves to bootstrap all the application and is the root of the application. All the *selectors* for the other components are located now in the `app.component.html`.

Good practice to create a new component, you should create a directory in the app folder and name it the same as the componentname. The convention of naming the component is like this `name.component.ts`. 

A component is a class which angular is able to instanciate.

Required files for a component are a `server.component.ts` and a `server.component.html`.

In the *.ts file goes the logic and in the *.html file is the template of the component.

```ts
import { Component } from '@angular/core'; // Import for the Component-Decorator

@Component({ // Decorator
    selector: 'app-server', // Unique selector
    templateUrl: './server.component.html' // template file
})

export class ServerComponent { // Component-Class

}
```

This register the component and let angular know that a new component was created, it needs to be declared in the root app module (`app.module.ts`). Add it in the `declarations`-array and for TS to find the file, it needs also an import.

<img src="../img/app-module.png" alt="app-module" width="600"/><br>

By adding the component-Tag to the `app.component.html` the component will be inbedded in the app.

```html
<app-server></app-server>
```

A component can be created with the ancular CLI
```bash
# long
ng generate component <name>

# short
ng g c <name>
```

This command will create a new folder and automatically update the `app.module`.

A component can be Nested. *Server* will be moved to the *Servers*. So that in the Dom we finde a wrapper arround the *Server-Component*:

<img src="../img/serversComponent.png" alt="app-servers" width="650"/><br>

### Selector

Angular have multiple ways to select the component (CSS-Selectors):
- by element `<app-server></app-server>`
- by attribute `[app-server]`
- by class `.app-server`

## Databinding

What is Databinding? Communication between TS-Code (Businessloginc) and the Template (HTML).

<img src="../img/databinding.png" alt="databinding" width="650"/><br>

## String Interpolation

With Databinding can be used to dynamically load data into the HTML-template. For example like this:
```html
<p>{{ 'server' }} with ID {{ serverID }} is {{ serverStatus }}</p>
```

In the `{{ }}` can be executed an TS Expression wich can be a simple property like `serverID`, `serverStatus` or any **Method** which returns a **string**.
Note that a number can easily be converted into a string, so there is no need to explicitly convert it.

The `{{ 'server' }}` is just a string output.

**Useage:**<br>
To pront some text in the template use String interpolation.

## Property Binding

`[ ]` indicates that we want to use a property binding.

Exsample to activate a Button after 2seconds:

servers.component.html
```ts
<button
    [disabled="!allowNewServer"]>Add Server</button>
```

servers.component.ts
```ts
export class ServerComponent implements OnInit {
    allowNewServer = false;

    constructor(){
        setTimeout(() => {
            this.allowNewServer = true;
        }, 2000);
    }
}
```

**Usage:**<br>
Change something dynamically upon an element use Property Binding.

```html
<p [innerText]="!allowNewServer"></p>
```

This syntax is recognized by angular. You cant mix with the curlybraces from the string interpolation. String interpolation is a TS feature.

## Event binding

**Syntax:**
```html
(event)="methodeToCall()"
```

**Example:**<br>
```html
<button
    [disabled="!allowNewServer"]
    (click)="onCreateServer()">Add Server</button>

<p>{{ serverCreationStatus }}</p>
```

## Passing and Using Data with Event binding

With the keyword `$event` we can extract lots of data from this object of type Event.

server.component.ts
```ts
...
    onUpdateServerName(event: Event) {
        this.serverName = (<HTMLImputElement>event.target).value;
    }
...
```

server.component.html
```html
...
<input
    type="text"
    (input)="onUpdateServerName($event)">
<p>{{ serverName }}</p>
...
```

## Two-Way-Databinding

Important: For Two-Way-Binding to work, you need to enable the `ngModel`  directive. This is done by adding the `FormsModule` to the `imports[]`  array in the **AppModule**.

You then also need to add the import from @angular/forms  in the app.module.ts file:

```ts
import { FormsModule } from '@angular/forms'; 
```

**Syntax:**
```html
[(ngModel)]=""
```

Updates the Input or Target based on eather one is changed.

## Directives

Directives are Instructions in the DOM. 

<img src="../img/directives.png" alt="directives" width="400"/><br>

Angular Documentation of [Built-in directives](https://angular.io/guide/built-in-directives)

## ngIf

Built-In directive which binds the data based on a condition. This

## ngStyle

Changes a CSS style attribute

## ngClass

Adds or removes a CSS-Class from the element.

## ngFor

Adds an ammount of elements to the DOM.
```html
<app-server *ngFor="let server of servers"><(app-server)>
```