Basics

Basics
Databinding
Directives deep dive
Services
Routing
Observables
Forms
- Template Driven Approach
- Reactive Approach
Pipes
Http requests
OTHER STUFF
- TODO
- TODO
- TODO
- TODO
Unit Testing

Basics

in console: create app

ng new myapp cd myapp ng serve

in angular.json

add this to styles to use bootstrap "node_modules/bootstrap/dist/css/bootstrap.min.css",

create component in cli ng generate component servers OR ng g c servers

it automatically updates the declaration in the app.module.ts

data binding

from ts to html

string interpolation {{ myvar }} in the html references myvar in ts property binding [property]="data"

Note in some cases they can be equivalent <p>{{ myvar }}</p> <=> <p [innerText]="myvar"></p>

from html to ts

event binding (event)="expression" $event keyword in html references the event

two way binding

[(ngModel)] = "data" need forms module in app.component.ts import { FormsModule } from '@angular/forms'

constructor

constructor is called on creation of element

Directives

if directive : it has a star because it is a structural directive

<p *ngIf="this.serverCreated; else noServer">
  Server {{ serverName }} was created
</p>
<ng-template #noServer>
  <p>no server was created</p>
</ng-template>

for loop : servers here is an array

<app-server *ngFor="let server of servers"></app-server>

attribute directive : only change element they were placed on (no start)

<p [ngStyle]="{backgroundColor: getColor()}">Example</p>

add or remove class based on truthy value

<p
  [ngClass]="{online: serverStatus === 'online', offline: serverStatus === 'offline'}"
></p>

example of for with index

<p *ngFor="let c of clickArr; let i = index;" [ngClass]="{'colored': i >= 5 }">
  {{c}} --- {{i}}
</p>

ts classes

export class Ingredient {
  public name: string;
  public amount: number;

  constructor(name: string, amount: number) {
    this.name = name;
    this.amount = amount;
  }
}

// * same as writing
export class Ingredient {
  constructor(public name: string, public amount: number) {}
}

Databinding

pass data to child component = custom property binding

in parent :

export class AppComponent {
  serverElements = [
    {
      type: 'server',
      name: 'TestServer',
      content: 'Just a test',
    },
  ];
}

<app-server-element
  *ngFor="let serverElement of serverElements;"
  [element]="serverElement"
></app-server-element>

in child : use Input decorator to expose element to the world

export class ServerElementComponent implements OnInit {
  @Input()
  element: {
    type: string;
    name: string;
    content: string;
  };

  constructor() {}

  ngOnInit(): void {}
}

Note use @Input("myalias") to bind to [myalias] in parent component

pass data to parent component -custom event emitter

In parent :

<app-cockpit (serverAdded)="onServerAdded($event)"></app-cockpit>

 onServerAdded(serverData: { serverName: string; serverContent: string }) {
    this.serverElements.push({
      type: "server",
      name: serverData.serverName,
      content: serverData.serverContent,
    });
  }

In child :

<button
    class="btn btn-primary"
    (click)="onAddServer()">Add Server</button>
<button

export class CockpitComponent implements OnInit {
  @Output()
  serverAdded = new EventEmitter<{
    serverName: string;
    serverContent: string;
  }>();

  constructor() {}
  ngOnInit(): void {}
  onAddServer() {
    this.serverAdded.emit({
      serverName: this.newServerName,
      serverContent: this.newServerContent,
    });
  }
}

Note : use @Output("myalias") to bind to (myalias) in parent component

encapsulation :

angular adds these attributes to the DOM _ngcontent-hpn-c41 They depend on the component

If I pass encapsulation: ViewEncapsulation.None then they are not applied and the style defined in the css of the component are passed globally

encapsulation: ViewEncapsulation.Native should give the same results as Emulated (default value) but only on browser that support the shadow DOM

local reference in templates

add a #myname in a html element to reuse it inside the html template :

<input type="text" class="form-control" #serverNameInput />
<button class="btn btn-primary" (click)="onAddServer(serverNameInput)">
  Add Server
</button>

and in ts

onAddServer(nameInput: HTMLInputElement) {
    this.serverAdded.emit({
      serverName: nameInput.value,
      serverContent: this.newServerContent,
    });
  }

Viewchild

lots of use (with local ref, or with component name directly) Most used case = with local ref. Ex below

Unlike the local reference passed in the template that referenced the html element itself, when we pass the local ref in ViewChild, it is of type ElementRef

<input type="text" class="form-control" #serverContentInput />

@ViewChild("serverContentInput") servContent: ElementRef;

onAddServer(nameInput: HTMLInputElement) {
    this.serverAdded.emit({
      serverName: nameInput.value,
      serverContent: this.servContent.nativeElement.value,
    });
  }

Note : do not change the element through this, it is bad. Angular offers a better way to access the DOM

projecting content with ng-content

by default, what is between two components html tags is not shown. Except if you put a ng-content

ex : in parent

<app-child>Extra content</app-child>

in child:

<p>Regular content</p>
<ng-content></ng-content>

Component lifecycle

ngOnChanges called after a bound input property changes <- properties decorated with @Input / receives an argument of type SimpleChanges
ngOnInit called once the component is initialized <- runs after the constructor
ngDoCheck called during every change detection run <- is called a lot
ngAfterContentInit called after content (ng-content) has been projected into view
ngAfterContentChecked called every time the projected content has been checked (by angular change detection)
ngAfterViewInit called after the component's view (and child views) has been initialized
ngAfterViewChecked called every time the view (and child views) have been checked
ngOnDestroy called once the component is about to be destroyed

Note : not possible to access templates ref before ngAfterViewInit

ContentChild

same as view child in parent :

<p #contentParagraph>Extra content</p>

in child html :

<ng-content></ng-content>

In child ts :

@ContentChild("contentParagraph", { static: true }) paragraph: ElementRef;

Can be accessed on ngAfterContentInit

Directives deep dive

attribute : only affect the element they are on
structural : affect the dom

Note : you cant have more than one structural directive on an element (no *ngFor + *ngIf)

Custom directive

import { Directive, ElementRef, Renderer2 } from '@angular/core';

@Directive({
  selector: '[appBetterHighlight]',
})
export class BetterHighlightDirective {
  constructor(private elRef: ElementRef, private renderer: Renderer2) {}
  ngOnInit() {
    this.renderer.setStyle(
      this.elRef.nativeElement,
      'background-color',
      'blue'
    );
  }
}

In app.module.ts, i need to import and declare it To use it, no square bracket

<p appBetterHighlight>Style me with better directive</p>

Note : Generate a directive with ng g d Note : renderer is the preferred way to change style because angular is not limited to the browser and can work in services who have no access to the dom

host listener

host listener to listen to events in directives

@HostListener("mouseenter") mouseover(eventData: Event) {
    this.renderer.setStyle(
      this.elRef.nativeElement,
      "background-color",
      "blue"
    );
  }

host binding

host binding to bind a property of the element the directive is applied to

@HostBinding("style.backgroundColor") backgroundColor: string;

Custom property binding in directive :

in the directive ts file I can add input and then use a custom property binding on the element where there is the directive

@Input() defaultColor: string = "transparent";
@Input() highlightColor: string = "blue";

<p appBetterHighlight [defaultColor]="'yellow'" [highlightColor]="'red'">
  Style me with better directive
</p>

Another solution if i have one main input; I can put directive between []

@Input("appBetterHighlight") highlightColor: string = "blue";

<p [appBetterHighlight]="'red'" [defaultColor]="'yellow'">
  Style me with better directive
</p>

Note : in angular, if we pass a string, we can omit the [] if we omit the '' : example [defaultColor]="'yellow'" is the same as defaultColor="yellow"

Structural directives : behind the scenes

for structural directives, behind the scene, angular does not know *. In fact it transforms

<div *ngIf="!onlyOdd">
  <li
    class="list-group-item"
    *ngFor="let even of evenNumbers"
    [ngClass]="{odd:even % 2 !== 0}"
  >
    {{ even }}
  </li>
</div>

into

<ng-template [ngIf]="!onlyOdd">
  <div>
    <li
      class="list-group-item"
      *ngFor="let even of evenNumbers"
      [ngClass]="{odd:even % 2 !== 0}"
    >
      {{ even }}
    </li>
  </div>
</ng-template>

So it is just a custom property binding in fact. And that explains the ng-template with the else

Example below : use with *appUnless="condition"

import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core';

@Directive({
  selector: '[appUnless]',
})
export class UnlessDirective {
  @Input() set appUnless(condition: boolean) {
    if (!condition) {
      this.vcRef.createEmbeddedView(this.templateRef);
    } else {
      this.vcRef.clear();
    }
  }

  constructor(
    private templateRef: TemplateRef<any>,
    private vcRef: ViewContainerRef
  ) {}
}

ngSwitch

<div [ngSwitch]="value">
  <p *ngSwitchCase="5">Value is 5</p>
  <p *ngSwitchCase="10">Value is 10</p>
  <p *ngSwitchCase="100">Value is 100</p>
  <p *ngSwitchDefault>Value is Def</p>
</div>

Services

they are standard class you put in a file : **.service.ts

Creation

export class LoggingService {
  logStatusChange(status: string) {
    console.log(`A server status changed, new status: ${status})`);
  }
}

Note : do not import the class and create a new instance when you want to use it, Angular has a built in way to get access to services.

Instead, you should import the service and put it in the constructor of your component and the providers

import { Component, EventEmitter, Output } from '@angular/core';
import { LoggingService } from '../logging.service';

@Component({
  selector: 'app-new-account',
  templateUrl: './new-account.component.html',
  styleUrls: ['./new-account.component.css'],
  providers: [LoggingService],
})
export class NewAccountComponent {
  @Output() accountAdded = new EventEmitter<{ name: string; status: string }>();

  constructor(private loggingService: LoggingService) {}

  onCreateAccount(accountName: string, accountStatus: string) {
    this.accountAdded.emit({
      name: accountName,
      status: accountStatus,
    });
    this.loggingService.logStatusChange(accountStatus);
  }
}

Hierarchichal injector

When you create a service, Angular knows how to create the service for the component and also ALL the child components !

Hierarchichal injector: where to provide the service

AppModule : same instance of Service is available Application-wide
AppComponent: same instance of Service is available for all Components but not for other services
Any component: same instance of service is available for the component and all children components (and children of children)
Note : if you provide a service to a component and its child, the service provided in the child overwrites the one provided in the parent (new instance) To use the instance of a parent, keep it in the constructor of the child but remove it from the providers list

New syntax for application wide services : Instead of adding a service class to the providers[] array in AppModule , you can set the following config in @Injectable() :

@Injectable({providedin: 'root'})
export class myservice { ... }

This is exactly the same as:

export class MyService { ... }

and

import { MyService } from './path/to/my.service';

@NgModule({
    ...
    providers: [MyService]
    })
export class AppModule { ... }

To inject a service into a service, i need to provide it at app.module level and add @Injectable() on the service where i want to RECEIVE another service. Alternatively, I can use Injectable with @Injectable({providedin: 'root'}) so that I dont have to declare it in app.module.ts

Note : you need injectable if you inject in the service, not if you inject the service somewhere else

Cross component communication

create a subject in the service
emit event in component A
subscribe to event in component B (in constructor for ex)
Note: it is better to use subject than EventEmitter

service :

import { Subject } from 'rxjs'
...
statusUpdated = new Subject<string>();

comp A:

this.accountsService.statusUpdated.next(status);

comp B:

ngOnInit() {
  this.accountsService.statusUpdated.subscribe(
    (status:string)=>{alert(`New status ${status}`)}
  )

Routing

imports

in app.module.ts

import { RouterModule, Routes } from '@angular/router';

then

const appRoutes: Routes = [
  { path: '', component: HomeComponent },
  { path: 'users', component: UsersComponent },
  { path: 'servers', component: ServersComponent },
];

then in @NgModule, imports: [BrowserModule, FormsModule, RouterModule.forRoot(appRoutes)],

in app.component.ts use

<router-outlet></router-outlet>

to render your routes In the example above, i can access my UsersComponent by going to /users

Implementing navigation :

do not just put a link with href as it will reload the app Instead: use the routerLink directive

<li role="presentation">
  <a routerLink="/servers">Servers</a>
</li>

or

<li role="presentation">
  <a [routerLink]="['/users', 'something']">Users</a>
</li>

Note : relative path can be used without the / or with ./ It is also possible to use ../

Attach a class to active route

routerLinkActive directive to attach a given class: note that by default, all the routes containing the path are active.

<li role="presentation" routerLinkActive="active">
  <a routerLink="/servers">Servers</a>
</li>

It is possible to add additionnal config to fix this

<li
  role="presentation"
  routerLinkActive="active"
  [routerLinkActiveOptions]="{ exact: true }"
></li>

Accessing router in ts file

import { Router } from '@angular/router';
...
export class HomeComponent implements OnInit {
  constructor(private router: Router) {}

  ngOnInit() {}
  onLoadServers() {
    // do sthg
    this.router.navigate(['/servers']);
  }
}

Note : unlike routerLink, this.router.navigate does not know on what route I am so I can omit the first /

If i want a relative route:

import { ActivatedRoute, Router } from '@angular/router';
constructor(..., private route: ActivatedRoute)

 onReload() {
    console.log('reload');
    this.router.navigate(['./'], { relativeTo: this.route });
  }

Passing parameters

in app.module, add this route with :id

{ path: 'users/:id', component: UserComponent },

then in your component

constructor(private route: ActivatedRoute) {}

ngOnInit() {
  this.user = {
      id: this.route.snapshot.params['id'],
    };
  }

potential error : if i reacess the same component for ex with

<a [routerLink]="['/users', 10, 'Anna']">Load Anna (10)</a>,

then when I click on the link, the route is changed but the component is NOT rerendered as it is on the same route, which means ngOnInit is not executed So in ngOnInit, it is fine to use the snapshot approach. But we must add something to react to changes

this.route.params.subscribe((params: Params) => {
  this.user.id = params['id'];
  this.user.name = params['name'];
});

it is good to implement the onDestroy lifecycle to remove the subscription when component is destroyed (though for routes it is not required as angular handles it). Final code :

import { Component, OnDestroy, OnInit } from '@angular/core';
import { ActivatedRoute, Params } from '@angular/router';
import { Subscription } from 'rxjs/Subscription';

@Component({
  selector: 'app-user',
  templateUrl: './user.component.html',
  styleUrls: ['./user.component.css'],
})
export class UserComponent implements OnInit, OnDestroy {
  user: { id: number; name: string };
  paramSubscription: Subscription;
  constructor(private route: ActivatedRoute) {}

  ngOnInit() {
    this.user = {
      id: this.route.snapshot.params['id'],
      name: this.route.snapshot.params['name'],
    };
    this.paramSubscription = this.route.params.subscribe((params: Params) => {
      this.user.id = params['id'];
      this.user.name = params['name'];
    });
  }
  ngOnDestroy() {
    this.paramSubscription.unsubscribe();
  }
}

Query parameters

<a
  [routerLink]="['/servers', 5, 'edit']"
  [queryParams]="{allowEdit:1}"
  [fragment]="'loading'"
  href="#"
  class="list-group-item"
  *ngFor="let server of servers"
>
  {{ server.name }}
</a>

links to

/servers/5/edit?allowEdit=1#loading

TO do it in a ts file :

onLoadServer(id: number) {
  this.router.navigate(['/servers', id, 'edit'], {
    queryParams: { allowEdit: 1 },
    fragment: 'loading',
    });
  }

Retrieve query parameters and fragment:

first approach, in ngOnInit: this.route.snapshot.queryParams and this.route.snapshot.fragment

To react on changes, same logic as before, we can subscribe this.route.queryParams.subscribe() and this.route.fragment.subsribe()

NOTE : params are recovered as string. To get them as nb, you can do +this.route.snapshot.params['id']

Nested routes :

possibility to add children in routes. Then in coresponding component, we must add a

const appRoutes: Routes = [
  { path: '', component: HomeComponent },
  {
    path: 'users',
    component: UsersComponent,
    children: [{ path: ':id/:name', component: UserComponent }],
  },
  {
    path: 'servers',
    component: ServersComponent,
    children: [
      { path: ':id', component: ServerComponent },
      { path: ':id/:name', component: EditServerComponent },
    ],
  },
];

query params handling when changing route

this.router.navigate(['edit'], {
  relativeTo: this.route,
  queryParamsHandling: 'merge',
}); // merge with queryParams of next route
this.router.navigate(['edit'], {
  relativeTo: this.route,
  queryParamsHandling: 'preserve',
}); // keeps queryparams of previous route

redirect

{ path: 'not-found', component: PageNotFoundComponent },
{ path: 'something', redirectTo: "not-found"},

// Note : if you want full path matching
{ path: '', redirectTo: '/somewhere-else', pathMatch: 'full' }

--- wildcard redirect :

{ path: '**', redirectTo: "not-found"},

BE SURE THIS ROUTE IS THE LAST

outsourcing the route config

in app-routing.module.ts

import ...

const appRoutes: Routes = [
  ... all the paths
];

@NgModule({
  imports: [RouterModule.forRoot(appRoutes)],
  exports: [RouterModule], // exposes the router to the other modules
})
export class AppRoutingModule {}

in app.module.ts

imports: [BrowserModule, FormsModule, AppRoutingModule],

guard : code executed on access / leave of route

First create a guard with a canActivate method for ex:

import { Injectable } from '@angular/core';
import {
  ActivatedRouteSnapshot,
  CanActivate,
  RouterStateSnapshot,
  Router,
} from '@angular/router';
import { Observable } from 'rxjs/Observable';
import { AuthService } from './auth-service';

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private authService: AuthService, private router: Router) {}

  canActivate(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<boolean> | Promise<boolean> | boolean {
    return this.authService.isAuthenticated().then((authenticated: boolean) => {
      if (authenticated) {
        return true;
      } else {
        this.router.navigate(['/']);
      }
    });
  }
}

Add this in the route where we want to protect : canActivate: [AuthGuard],

Note : remember to add the imported services to app.module.ts

protect child routes

Same logic but we create a function called canActivateChild and put it into the route

protect exit from route with canDeactivate:

It is a bit more complex as the CanDeactivate interface needs a component. A generic way to implement it would be to create a file can-deactivate-guard.service.ts

import {
  ActivatedRouteSnapshot,
  RouterStateSnapshot,
  Router,
  CanDeactivate,
  UrlTree,
} from '@angular/router';
import { Observable } from 'rxjs/Observable';

export interface CanComponentDeactivate {
  canDeactivate: () =>
    | Observable<boolean | UrlTree>
    | Promise<boolean | UrlTree>
    | boolean
    | UrlTree;
}

export class CanDeactivateGuard
  implements CanDeactivate<CanComponentDeactivate>
{
  canDeactivate(
    component: CanComponentDeactivate,
    currentRoute: ActivatedRouteSnapshot,
    currentState: RouterStateSnapshot,
    nextState?: RouterStateSnapshot
  ):
    | Observable<boolean | UrlTree>
    | Promise<boolean | UrlTree>
    | boolean
    | UrlTree {
    return component.canDeactivate();
  }
}

And then in the component where i want to implement the guard, i implement the canDeactivate method with no args

 canDeactivate():
    | Observable<boolean | UrlTree>
    | Promise<boolean | UrlTree>
    | boolean
    | UrlTree {
    if (!this.allowEdit) {
      return true;
    } else {
      if (
        this.serverName !== this.server.name ||
        (this.serverStatus !== this.server.status && !this.changesSaved)
      ) {
        return confirm('Do you want to discard the changes?');
      } else {
        return true;
      }
    }
  }

And then i add it to the app-routing.module and the providers of app.module

Note : it i want to tie the canDeactivate to a specific component, i can use it directly instead of creating the CanComponentDeactivate interface

passing static data to a route

in app-routing:
 {
    path: 'not-found',
    component: ErrorPageComponent,
    data: { message: 'Page Not Found!' },
  },

in component : either option 1 or commented option works

  ngOnInit(): void {
	  this.errorMessage = this.route.snapshot.data["message"]
	//   this.route.data.subscribe(( data:Data )=>{
	// 	  this.errorMessage = data["message"]
	//   })
  }

passing dynamic data : use of a resolve service :

import { Injectable } from '@angular/core';
import {
  ActivatedRouteSnapshot,
  Resolve,
  RouterStateSnapshot,
} from '@angular/router';
import { Observable } from 'rxjs/Observable';
import { ServersService } from '../servers.service';

interface Server {
  id: number;
  name: string;
  status: string;
}

@Injectable()
export class ServerResolver implements Resolve<Server> {
  constructor(private serversService: ServersService) {}

  resolve(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<Server> | Promise<Server> | Server {
    return this.serversService.getServer(+route.params['id']);
  }
}

Then i add it to the providers in app.module Then in app-routing.module:

{ path: ':id', component: ServerComponent, resolve: {server: ServerResolver} }

and in my component, i subscribe to the route data

ngOnInit() {
  this.route.data.subscribe((data: Data)=>{
    this.server = data["server"]
  })
}

---- LOCATION STRATEGY the server must be configured so that a 404 returns the index html so that angular can then parse the route Alternative approach using a hash sign : in app.routing, you can pass an arg to RouterModule.forRoot : {useHash: True}

Observables

theory

An observable is a datasource (events, http requests, triggered in code..)

An observer is our code : for ex our subscribe functions Three ways to handle it:

handle data
handle error
handle completion

Note: some observables never complete; Others such as http requests will complete eventually Observables are another approach at handling asynchronous events

route params observable :

ngOnInit() {
  this.route.params.subscribe((params: Params) => {
    this.id = +params.id;
  });
}

Here params is a built in observable and subscribe is our observer.

subscribe/unsubscribe

Observables are not core js/ts features. Instead they come from a package called rxjs

example :

import { interval } from 'rxjs';
...
ngOnInit() {
  interval(1000) // fires an event every second
  .subscribe((count) => {
    console.log(count);
  });
}

interval fires an event each 1000 ms here. When i navigate away from my component, it keeps on counting. Note : certain observables emit values only once such as an http request but some of them will keep emitting values even if you are not interested in them anymore. To prevent memory leaks you must unsubsribe to observables you are not interested in anymore. Final implementation :

import { Component, OnInit, OnDestroy } from '@angular/core';
import { interval, Subscription } from 'rxjs';
...
export class HomeComponent implements OnInit, OnDestroy {
  private firstObsSubscription: Subscription;
  constructor() {}

  ngOnDestroy() {
    this.firstObsSubscription.unsubscribe();
  }

  ngOnInit() {
    this.firstObsSubscription = interval(1000).subscribe((count) => {
      console.log(count);
    });
  }
}

Note : observables provided by angular (such as route.params) are managed by angular and will therefore be unsubscribed automatically

Custom observable

To build the same interval manually :

import {  Observable } from 'rxjs';
...

export class HomeComponent implements OnInit, OnDestroy {
  ...
  ngOnInit() {
    const customIntervalObservable = Observable.create((observer) => {
      let count = 0;
      setInterval(() => {
        observer.next(count);
        if (count >3){
          observer.error(new Error("Count is greater than 3"))
		}
        count += 1;
      }, 1000);
    });

    this.firstObsSubscription = customIntervalObservable.subscribe(count={
      console.log(count)
	},
    error=>{
      console.log(error)
	})
  }
}

the observer has three differents methods :

next : emits the next event
error
complete

error and completion

After an error, the observable stops emitting. Error should be handled :

  ngOnInit() {
    const customIntervalObservable = Observable.create((observer) => {
      let count = 0;
      setInterval(() => {
        observer.next(count);
		if (count == 2) observer.complete()
        if (count > 3) {
          observer.error(new Error('Count is greater than 3'));
        }
        count += 1;
      }, 1000);
    });

    this.firstObsSubscription = customIntervalObservable.subscribe(
      (count) => {
        console.log(count);
      },
      (error) => {
        console.log(error);
        alert(error.message);
      }
    );
  }

Observables such as Http requests automatically complete. On the other hand, interval never completes. To complete our custom observable,

if (count === 2) observer.complete();

this.firstObsSubscription = customIntervalObservable.subscribe(
  (count) => {
    console.log(count);
  },
  (error) => {
    console.log(error);
    alert(error.message);
  },
  // completion handler function (no arg)
  () => {
    console.log('Cleaning up');
  }
);

Now we dont have the error at count >3 because it stops emitting when complete is called

NOTE : after completion or error, no need to unsubscribe, but we can add the unsubscription anyways VERY IMPORTANT : completion is not fired in case of error

Operators

Magic feature of rxjs library You can use operators between the observable and the subscriptions. Which means the datapoints first reach the operators before the subscription. So you can subscribe to the result of these operators Operators are used with pipe; Every observable has a pipe method

import { map } from 'rxjs/operators';
...
this.firstObsSubscription = customIntervalObservable
.pipe(
  map((data: number) => {
    return 'Round: ' + (data + 1);
  })
)
.subscribe(...);
  }

Now the map operator allow us to transform the data before receiving it in the subscribe method You can chain arguments in pipe. List here https://www.learnrxjs.io/learn-rxjs/operators

import { map, filter } from 'rxjs/operators';
...

.pipe(
  filter((data) => {
    return data > 0; // return true or false
  }),
  map((data: number) => {
    return 'Round: ' + (data + 1);
  })
)

Subjects

Functions the same way as event emitter (approximation). Should be used in cross component communication : seems like they are more efficient In the service :

import { Injectable } from '@angualr/core';
import { Subject } from 'rxjs';

@Injectable({ provideIn: 'root' })
export class MyService {
  myEmitter = new Subject<number>();
}

In the component where you emit

constructor(private myService: Myservice){}
...
this.myService.myEmitter.next(true)

In the component where you subscribe

constructor(private myService: Myservice){}
...
ngOnInit(){
  this.myService.myEmitter.subscribe(data=> console.log(data))
}

In observables, we could call next from the inside but with Subject, i can call next from the outside, which is why i can call next from a component, which makes it perfect as an event emitter. Rule :

only use event emitter in conjuction with @Output
for cross component communication, use Subject Note : same as observable, you can use operators Dont forget to unsubscribe in ngOnDestroy

Forms

Template Driven Approach

Form Basics

In app.module.ts

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

Now, each time there is a form element in the code, angular will automatically create a js object representing the form.

In the html file

<form>
  <div id="user-data">
    <div class="form-group">
      <label for="username">Username</label>
      <input
        type="text"
        id="username"
        class="form-control"
        ngModel
        name="username"
      />
    </div>
    <button class="btn btn-default" type="button">Suggest an Username</button>
    <div class="form-group">
      <label for="email">Mail</label>
      <input
        type="email"
        id="email"
        class="form-control"
        ngModel
        name="email"
      />
    </div>
  </div>
  <div class="form-group">
    <label for="secret">Secret Questions</label>
    <select id="secret" class="form-control" ngModel name="secret">
      <option value="pet">Your first Pet?</option>
      <option value="teacher">Your first teacher?</option>
    </select>
  </div>
  <button class="btn btn-primary" type="submit">Submit</button>
</form>

First thing to note : no method / action specified in the form because Angular will handle the form
Rest of the form is standard html form
Add controls to the angular js object with ngModel. Note that we do not use [()]. We also need to add the name attribute

Getting the js object

To submit the form, we should NOT add a click listener to the submit button. Doing so will trigger standard form behavior (a submit event). Instead, we should put the ngSubmit event directly on the form. This event will be fired when we click submit

<form (ngSubmit)="onSubmit(myform)" #myform="ngForm"></form>

import { NgForm } from '@angular/forms';

  onSubmit(f:NgForm) {
    console.log(f);
  }

Note: in the template, arg of on submit must have same name as template ref
Note 2: the ="ngForm" tels angular to get the form js object
The form object has a lot of properties. The values entered by the user are in the value attribute

Another way to submit with ViewChild

<form (ngSubmit)="onSubmit()" #myform="ngForm"></form>

import { NgForm } from '@angular/forms';

@ViewChild('myform') myform: NgForm;
onSubmit() {
    console.log(this.myform);
}

Instead of passing myform to submit, we instead use the ref to get it via ViewChild This is useful if we want to access the form before submit

Reactive Approach

Pipes

Main purpose

Transform output in your templates For ex, in your template, use the builtin uppercase pipe :

<p>{{ username | uppercase}}</p>

it will modify what is shown without modifying the property Note : | is a symbol called "pipe" hence the name "pipes"

Parametrizing Pipes

To configure a pipe, you add a : Example with the built in date pipe :

{{ server.started | date:'fullDate' }}

Note : if a pipe takes several parameters, you would do something like

{{ myproperty | mypipe:'value1':'value2' }}

Where to learn more

https://angular.io/api?type=pipe for ex, the slice pipe :

{{ value_expression | slice : start [ : end ] }}

Chaining multiple pipes

{{ server.started | date:'fullDate' | uppercase}}

Order is important (generally parsed from left to right)

Creating a custom pipe :

shorten.pipe.ts

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'shorten',
})
export class ShortenPipe implements PipeTransform {
  transform(value: any, nbCharacters: number = 10) {
    return value.substr(0, nbCharacters);
  }
}

in app.module.ts, add ShortenPipe in declarations in component, use like this for default value

{{ server.name | shorten }}

or like this to specify nb characters

{{ server.name | shorten:4 }}

Creating a filter pipe

Generate pipe with cli : ng g p

By default angular is not rerunning the pipe on the data whenever the data changes To be precise, updating arrays or object does not trigger it However it does run it again when the inputs of the pipe change. If you want it to be triggered on any change in the page data :

@Pipe({
  name: 'filter',
  pure: false,
})

However, it can lead to performance issues so be careful. Ex of a filter pipe :

export class FilterPipe implements PipeTransform {
  transform(value: any, filterString: string, propName: string): any {
    if (value.length === 0 || filterString === '') {
      return value;
    }
    const resultArray = [];
    for (const item of value) {
      if (item[propName] === filterString) {
        resultArray.push(item);
      }
    }
    return resultArray;
  }
}

<div class="container">
  <div class="row">
    <div class="col-xs-12 col-sm-10 col-md-8 col-sm-offset-1 col-md-offset-2">
      <input type="text" [(ngModel)]="filteredStatus" />
      <br />
      <button class="btn btn-primary" (click)="onAddServer()">
        Add Server
      </button>
      <ul class="list-group">
        <li
          class="list-group-item"
          *ngFor="let server of servers | filter:filteredStatus:'status'"
          [ngClass]="getStatusClasses(server)"
        >
          <span class="badge"> {{ server.status }} </span>
          <strong>{{ server.name |shorten }}</strong> | {{ server.instanceType |
          uppercase }} | {{ server.started | date:'fullDate' | uppercase}}
        </li>
      </ul>
    </div>
  </div>
</div>

For pure pipes, if i add a server while the filter is on, i wont see it until I change the input. For impure pipes, i will see it directly

Async pipe

in my component:

export class AppComponent {
  appStatus = new Promise((resolve, reject)=>{
	  setTimeout(()=>{
		  resolve("stable")
	  }, 2000)
  })
  ...

in html

<h2>App status: {{ appStatus | async}}</h2>

the built in async pipe will recognize promises (and observables) and display the resulting value when the promise is finished

Http requests

Dont store credentials in angular

Create db service in firestore :

NOTE : this is not a database but a service. Angular should never communicated directly with a database

start in test mode https://ng-complete-guide-f3876-default-rtdb.firebaseio.com/

Sending post request

in app.module.ts

import { HttpClientModule } from '@angular/common/http';
@NgModule({
  ...
  imports: [..., HttpClientModule],
  ...
})

in component

import { HttpClient } from '@angular/common/http';

....

constructor(private http: HttpClient) {}

onCreatePost(postData: { title: string; content: string }) {
// angular automatically converts our js object to json
  this.http.post(this.baseUrl + "/posts.json", postData).subscribe(
    (res) => {
      // no need to unsubscribe as it completes anyways after res is sent
      console.log(res);
    },
  );
}

http requests are observables. Which means we have to subscribe to a http request. If not, it means we are not interested in the response and angular does not even send the request

Get requests

private fetchPosts() {
  this.http.get(this.baseUrl + '/posts.json').subscribe((posts) => {
    console.log(posts);
  });
}

the data we get is a bit messy, we have to transform it !

Using rxjs operators to transform response data

The data returned is in the form of nested object, so we use pipe to transform it.

private fetchPosts() {
  this.http
  .get(this.baseUrl + '/posts.json')
  .pipe(
    map((responseData) => {
      const postArray = [];
      for (const key in responseData) {
        if (responseData.hasOwnProperty(key)) {
          postArray.push({ ...responseData[key], id: key });
        }
      }
      return postArray;
    })
  )
  .subscribe((posts) => {
    console.log(posts);
  });
}

Types with http client

To get better autocompletion, you can do something like this :

this.http
  .get(this.baseUrl + '/posts.json')
  .pipe(
    map((responseData: { [key: string]: Post }) => {

However, with http client, there is a more elegant way. Instead the get method is a so called generic method

this.http
  .get<{ [key: string]: Post }>(this.baseUrl + '/posts.json')
  .pipe(
    map((responseData) => {

Note that this functionality is available for all http requests. For post requests, what we put between <> is the format of the response not the request body. In our case :

onCreatePost(postData: Post) {
  this.http.post<{name: string}>(...

Using services

Best practice : in service do http request and transformation of data. In component, subscribe to result

Service :

fetchPosts() {
  return this.http
    .get<{ [key: string]: Post }>(this.baseUrl + '/posts.json')
    .pipe(
      map((responseData) => {
        const postArray: Post[] = [];
        for (const key in responseData) {
          if (responseData.hasOwnProperty(key)) {
            postArray.push({ ...responseData[key], id: key });
          }
        }
        return postArray;
      })
    )
}

Component :

onFetchPosts() {
  this.isFetching = true;
  this.postsService.fetchPosts().subscribe((posts) => {
    this.loadedPosts = posts;
    this.isFetching = false;
  });
}

Delete request

clearPosts() {
  return this.http.delete(this.baseUrl + '/posts.json');
}

Error handling

Standard way

onFetchPosts() {
  this.isFetching = true;
  this.postsService.fetchPosts().subscribe((posts) => {
    this.loadedPosts = posts;
    this.isFetching = false;
  }, error =>{
	this.isFetching = false;
	console.log(error)
  });
}

With subject

useful if i dont subscribe in the component but in the service directly In the service

errorMessage = new Subject<string>();
...
createAndStorePost(title: string, content: string) {
  const postData: Post = {
    title: title,
    content: content,
  };
  this.http
    .post<{ name: string }>(this.baseUrl + '/posts.json', postData)
    .subscribe(
      (res) => {
        console.log(res);
      },
      (error) => {
        this.errorMessage.next(error.message);
      }
    );
}

In the component, I subscribe to errorMessage

catchError operator

import { catchError } from 'rxjs/operators';
import { throwError } from 'rxjs';
...
export class PostsService {

 ...

  fetchPosts() {
    return this.http
      .get<{ [key: string]: Post }>(this.baseUrl + '/posts.json')
      .pipe(
        map((responseData) => {
          const postArray: Post[] = [];
          for (const key in responseData) {
            if (responseData.hasOwnProperty(key)) {
              postArray.push({ ...responseData[key], id: key });
            }
          }
          return postArray;
        }),
        catchError((errorRes) => {
          console.log('Sending to analytics');
          // pass the errorRes: it needs to reach subscribe
          return throwError(errorRes);
        })
      );
  }

Setting headers

In the http request, we can add an options object (extra arg)

import { HttpHeaders } from '@angular/common/http';

...
this.http.get<{ [key: string]: Post }>(this.baseUrl + '/posts.json',
{
  headers: new HttpHeaders({"Custom-Header": "Hello"})
})

import { HttpParams } from '@angular/common/http';

Query params

this.http.get<{ [key: string]: Post }>(this.baseUrl + '/posts.json', {
  headers: new HttpHeaders({ 'Custom-Header': 'Hello' }),
  params: new HttpParams()
    .set('print', 'pretty') // overwrites values
    .append('search', 'mystring'), // add a new value
});

Observing different types of response.

Up until now, we only looked at the response body. But sometimes we need to look at the response headers or status for ex. So instead of only the body, we can get the full response. In the options object, i can add the observe key with :

'body' gives the default response
'response' gives the full response
'events' outputs all the events

this.http.post<{ name: string }>(this.baseUrl + '/posts.json', postData, {
  observe: 'response', // 'body' | 'events' | 'response' - 'body' by default
});

import { tap } from 'rxjs/operators';
import {HttpEventType} from '@angular/common/http';

...

return this.http
  .delete(this.baseUrl + '/posts.json', {
    observe: 'events',
  })
  .pipe(
    tap((event) => {
	  if (event.type === HttpEventType.Response){
		  console.log(event.body);
	  }
	  // don't return anything, it does alter the dataflow
    })
  );
}

tap allows to execute some code without altering the response HttpEventType is an enum :

Sent = 0,
UploadProgress = 1,
ResponseHeader = 2,
DownloadProgress = 3,
Response = 4,
User = 5

Response type

By default angular expects json. But we can chage the responseType in the options, for ex

{
  responseType: 'text'; // or 'json' or 'blob'
}

Interceptor

Providing the service

add some code each time a request leaves the app An interceptor is a service but the way we provide it is a bit different than usual.

For ex : in the service :

import {
  HttpHandler,
  HttpInterceptor,
  HttpRequest,
} from '@angular/common/http';

export class AuthInterceptorService implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler) {
    console.log('Request is on its way');
    return next.handle(req); // lets the request continue
  }
}

In app.module.ts

import {  HTTP_INTERCEPTORS } from '@angular/common/http';
...
@NgModule({
  ...
  providers: [
    {
      provide: HTTP_INTERCEPTORS, // special keyword
      useClass: AuthInterceptorService,
      multi: true, // allows multiple interceptors
    },
  ],
  ...

Modify the request object inside the interceptor

The request object is immutable and therefore, inside the interceptor, we can not do req.url = 'something' Instead, we call request.clone and pass a js object where we can overwrite all the core things For ex :

export class AuthInterceptorService implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler) {
    console.log('Request is on its way');
    const modifiedRequest = req.clone({
      headers: req.headers.append('Auth', 'xyz'),
    });
    return next.handle(modifiedRequest); // forwards the modified req
  }
}

Response interceptor

In the interceptor, you can interact with the request as shown above. You can also interact with the response :

return next
      .handle(modifiedRequest) // observable
      .pipe(
        tap((event) => {
          // no matter which responsetype you chose,
          // in interceptors you always get an event
          console.log('event', event);
          if (event.type == HttpEventType.Response) {
            console.log('Response arrived');
            console.log(event.body);
          }
        })
      );
  }

Multiple interceptors

in app.module

providers: [
    {
      provide: HTTP_INTERCEPTORS, // special keyword
      useClass: AuthInterceptorService,
      multi: true, // allows multiple interceptors
    },
    {
      provide: HTTP_INTERCEPTORS, // special keyword
      useClass: LoggingInterceptorService,
      multi: true, // allows multiple interceptors
    },
  ],

Note : the order is important

OTHER STUFF

TODO

Unit Testing

We use jasmine to test angular Just run ng test to launch the tests

Testing app.component

import { TestBed, async } from '@angular/core/testing';
import { AppComponent } from './app.component';

describe('App: CompleteGuideFinalWebpack', () => {
  beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [AppComponent],
    });
  });
  it('should create the app', async(() => {
    let fixture = TestBed.createComponent(AppComponent);
    let app = fixture.debugElement.componentInstance;
    expect(app).toBeTruthy();
  }));

  it(`should have as title 'app works!'`, async(() => {
    let fixture = TestBed.createComponent(AppComponent);
    let app = fixture.debugElement.componentInstance;
    expect(app.title).toEqual('app works!');
  }));
});

First TestBed is used for the testing; beforeEach is executed before each test (which are executed independently) Instructions are pretty straightforward

Testing a basic component

<div *ngIf="isLoggedIn">
  <h1>User logged in</h1>
  <p>User is: {{ user.name }}</p>
</div>
<div *ngIf="!isLoggedIn">
  <h1>User not logged in</h1>
  <p>Please log in first</p>
</div>

export class UserComponent implements OnInit {
  user: { name: string };
  isLoggedIn = false;
  constructor() {}
  ngOnInit() {}
}

Now lets test it

describe('Component: User', () => {
  beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [UserComponent],
    });
  });

  it('should create the app', () => {
    const fixture = TestBed.createComponent(UserComponent);
    const app = fixture.debugElement.componentInstance;
    expect(app).toBeTruthy();
  });
});

Same idea as app.component here

Testing dependencies: components and services

Lets create a service and provide it to the user component

export class UserService {
  user = {
    name: 'Gab',
  };
}

In the user component

constructor(private userService: UserService) {}

  ngOnInit() {
    this.user = this.userService.user;
  }

Now to test it, we need to get the username from the service

it('should use the user name from the service', () => {
  const fixture = TestBed.createComponent(UserComponent);
  const app = fixture.debugElement.componentInstance;

  const userService = fixture.debugElement.injector.get(UserService);
  expect(userService.user.name).toEqual(app.user.name);
});

Here i get an error and the test fails: app.user is undefined. Indeed, we missed the lifecycle hooks that happen automatically in angular. Indeed the user.name is set on ngOnInit; Here we have to run them ourselves. To fix this:

it('should use the user name from the service', () => {
    ...
    const userService = ...
	fixture.detectChanges();
	expect ...
  });

and now it works. To test now what is displayed, i need to access the template

it('should display the username if user is logged in', () => {
  const fixture = TestBed.createComponent(UserComponent);
  const app = fixture.debugElement.componentInstance;
  // no need to access the injected userService here because i dont want
  // to test it
  app.isLoggedIn = true; // modified the isLoggedIn attr
  fixture.detectChanges();
  let compiled = fixture.debugElement.nativeElement;
  expect(compiled.querySelector('p').textContent).toContain(app.user.name);
});

and of course

it("shouldn't display the username if user is not logged in", () => {
    ...
    // no overwriting of isLoggedIn here
    expect(compiled.querySelector('p').textContent).not.toContain(
      app.user.name
    );
  });

Name		Name	Last commit message	Last commit date
Latest commit History 120 Commits
.vscode		.vscode
angularapp		angularapp
cmpdatabinding		cmpdatabinding
directives		directives
forms		forms
http		http
observables		observables
pipes		pipes
recipe		recipe
routing		routing
services		services
testing		testing
.prettierrc.json		.prettierrc.json
readme.md		readme.md

Gabriel2409/angular

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Basics

data binding

from ts to html

from html to ts

two way binding

constructor

Directives

ts classes

Databinding

pass data to child component = custom property binding

pass data to parent component -custom event emitter

encapsulation :

local reference in templates

Viewchild

projecting content with ng-content

Component lifecycle

ContentChild

Directives deep dive

Custom directive

host listener

host binding

Custom property binding in directive :

Structural directives : behind the scenes

ngSwitch

Services

Creation

Hierarchichal injector

Cross component communication

Routing

imports

Implementing navigation :

Attach a class to active route

Accessing router in ts file

Passing parameters

Query parameters

Nested routes :

query params handling when changing route

redirect

outsourcing the route config

guard : code executed on access / leave of route

protect child routes

protect exit from route with canDeactivate:

passing static data to a route

passing dynamic data : use of a resolve service :

Observables

theory

route params observable :

subscribe/unsubscribe

Custom observable

error and completion

Operators

Subjects

Forms

Template Driven Approach

Form Basics

Getting the js object

Another way to submit with ViewChild

Reactive Approach

Pipes

Main purpose

Parametrizing Pipes

Where to learn more

Chaining multiple pipes

Creating a custom pipe :

Creating a filter pipe

Async pipe

Http requests

Create db service in firestore :

Sending post request

Get requests

Using rxjs operators to transform response data

Types with http client

Using services

Delete request

Error handling

Packages