Sometimes we need to work with every single Control is a form. Here's how it can be done:
function flattenControls(form: AbstractControl): AbstractControl[] {
let extracted: AbstractControl[] = [ form ];
if (form instanceof FormArray || form instanceof FormGroup) {
const children = Object.values(form.controls).map(flattenControls);
extracted = extracted.concat(...children);
}
return extracted;
}
For examples use:
// returns all dirty abstract controls
extractControls(form).filter((control) => control.dirty);
// mark all controls as touched
extractControls(form).forEach((control) =>
control.markAsTouched({ onlySelf: true }));
It's really easy to add keyboard shortcuts in the template:
<textarea (keydown.ctrl.enter)="doSomething()"></textarea>
<input (keydown.enter)="...">
<input (keydown.a)="...">
<input (keydown.esc)="...">
<input (keydown.shift.esc)="...">
<input (keydown.control)="...">
<input (keydown.alt)="...">
<input (keydown.meta)="...">
<input (keydown.9)="...">
<input (keydown.tab)="...">
<input (keydown.backspace)="...">
<input (keydown.arrowup)="...">
<input (keydown.shift.arrowdown)="...">
<input (keydown.shift.control.z)="...">
<input (keydown.f4)="...">
Every rendered angular component is wrapped in a host element (which is the same as component's selector).
It is possible to bind properties and attributes of host element using @HostBinding decorators, e.g.
import { Component, HostBinding } from '@angular/core';
@Component({
selector: 'my-app',
template: `
<div>Use the input below to select host background-color:</div>
<input type="color" [(ngModel)]="color">
`,
styles: [
`:host { display: block; height: 100px; }`
]
})
export class AppComponent {
@HostBinding('style.background') color = '#ff9900';
}
Generally we get one service instance per the whole application.
It is also possible to create an instance of service per component or directive.
@Component({
selector: 'provide',
template: '<ng-content></ng-content>',
providers: [ Service ]
})
export class ProvideComponent {}
@Directive({
selector: '[provide]',
providers: [ Service ]
})
export class ProvideDirective {}
It is possible to add global event listeners in your Components/Directives with HostListener. Angular will take care of unsubscribing once your directive is destroyed.
@Directive({
selector: '[rightClicker]'
})
export class ShortcutsDirective {
@HostListener('window:keydown.ArrowRight')
doImportantThings() {
console.log('You pressed right');
}
}
You can have multiple bindings:
@HostListener('window:keydown.ArrowRight')
@HostListener('window:keydown.PageDown')
next() {
console.log('Next')
}
You can also pass params:
@HostListener('window:keydown.ArrowRight', '$event.target')
next(target) {
console.log('Pressed right on this element: ' + target)
}
Sometimes you need to get access to global document.
To simplify unit-testing, Angular provides it through dependency injection:
import { DOCUMENT } from '@angular/common';
import { Inject } from '@angular/core';
@Component({
selector: 'my-app',
template: `<h1>Edit me </h1>`
})
export class AppComponent {
constructor(@Inject(DOCUMENT) private document: Document) {
// Word with document.location, or other things here....
}
}
Here is the way to notify user that there are fields with non-valid values.
markFieldsAsTouched function FormGroup or FormArray as an argument.
function markFieldsAsTouched(form: AbstractControl): void {
form.markAsTouched({ onlySelf: true });
if (form instanceof FormArray || form instanceof FormGroup) {
Object.values(form.controls).forEach(markFieldsAsTouched);
}
}
It's very useful to check out more general method Accessing all nested form controls by Thekiba to work with controls.
It's possible to take a template as @Input for a component to customize the render
@Component({
template: `
<nav>
<ng-container *ngTemplateOutlet="template"></ng-container>
</nav>
`,
})
export class SiteMenuComponent {
@Input() template: TemplateRef<any>;
}
<site-menu [template]="menu1"></site-menu>
<ng-template #menu1>
<div><a href="#">item1</a></div>
<div><a href="#">item2</a></div>
</ng-template>
Note:
ng-contentshould be used for most of the cases and it's simpler and more declarative.
Only use this approach if you need extra flexibility that can't be achieved with ng-content.
While the best way of reusing your code is creating a component, it's also possible to do it in a template.
To do this you can use ng-template along with *ngTemplateOutlet directive.
<p>
<ng-container *ngTemplateOutlet="fancyGreeting"></ng-container>
</p>
<button>
<ng-container *ngTemplateOutlet="fancyGreeting"></ng-container>
</button>
<ng-template #fancyGreeting>
Hello <b>{{name}}!</b>
</ng-template>
If you need a custom pipe, before creating one, consider checking out the NGX Pipes package which has 70+ already implemeted custom pipes.
Here are some examples:
<p>{{ date | timeAgo }}</p>
<!-- Output: "last week" -->
<p>{{ 'foo bar' | ucfirst }}</p>
<!-- Output: "Foo bar" -->
<p>3 {{ 'Painting' | makePluralString: 3 }}</p>
<!-- Output: "3 Paintings" -->
<p>{{ [1, 2, 3, 1, 2, 3] | max }}</p>
<!-- Output: "3" -->
You can use advanced property bindings to set specific style values based on component property values:
<p [style.background-color]="'green'">
I am in green background
</p>
<p [style.font-size.px]="isImportant ? '30' : '16'">
May be important text.
</p>
<!-- Width in pixels -->
<div [style.width.px]="pxWidth"></div>
<!-- Font size in percentage relative to the parent -->
<div [style.font-size.%]="percentageSize">...</div>
<!-- Height relative to the viewport height -->
<div [style.height.vh]="vwHeight"></div>
Similar to how you can two-way bind [(ngModel)] you can two-way bind custom property on a component, for example [(value)]. To do it use appropriate Input/Output naming:
@Component({
selector: 'super-input',
template: `...`,
})
export class AppComponent {
@Input() value: string;
@Output() valueChange = new EventEmitter<string>();
}
Then you can use it as:
<super-input [(value)]="value"></super-input>
For testing purposes you might want to inject window.location object in your component.
You can achieve this with custom InjectionToken mechanism provided by Angular.
export const LOCATION_TOKEN = new InjectionToken<Location>('Window location object');
@NgModule({
providers: [
{ provide: LOCATION_TOKEN, useValue: window.location }
]
})
export class SharedModule {}
//...
@Component({
})
export class AppComponent {
constructor(
@Inject(LOCATION_TOKEN) public location: Location
) {}
}
Enums are great but they are not visible in Angular templates by default.
With this little trick you can make them accessible.
enum Animals {
DOG,
CAT,
DOLPHIN
}
@Component({
...
})
export class AppComponent {
animalsEnum: typeof Animals = Animals;
}
Check out Angular Cheat Sheet or (alternative version) containing lots of useful information condensed in one place.
Also Angular Checklist contains is curated list of common mistakes made when developing Angular applications.
If you're using ViewEncapsulation value which is different than default, it might be daunting to set the value manually for every component.
Luckily you can configure it globally when bootstrapping your app:
platformBrowserDynamic().bootstrapModule(AppModule, [
{
// NOTE: Use ViewEncapsulation.None only if you know what you're doing.
defaultEncapsulation: ViewEncapsulation.None
}
]);
To act upon swipes, pans, and pinhces as well as the other mobile gestures, you can use hammerjs with HostListener decorator, or an event binding,
npm install hammerjs
@HostListener('swiperight')
public swiperight(): void {
// Run code when a user swipes to the right
}
Here are samples on how to use all of the hammerjs event bindings, you can use these events with a HostListener as well:
<!-- pan events -->
<div (pan)="logEvent($event)"></div>
<div (panstart)="logEvent($event)"></div>
<div (panmove)="logEvent($event)"></div>
<div (panend)="logEvent($event)"></div>
<div (pancancel)="logEvent($event)"></div>
<div (panleft)="logEvent($event)"></div>
<div (panright)="logEvent($event)"></div>
<div (panup)="logEvent($event)"></div>
<div (pandown)="logEvent($event)"></div>
<!-- pinch events -->
<div (pinch)="logEvent($event)"></div>
<div (pinchstart)="logEvent($event)"></div>
<div (pinchmove)="logEvent($event)"></div>
<div (pinchend)="logEvent($event)"></div>
<div (pinchcancel)="logEvent($event)"></div>
<div (pinchin)="logEvent($event)"></div>
<div (pinchout)="logEvent($event)"></div>
<!-- press events -->
<div (press)="logEvent($event)"></div>
<div (pressup)="logEvent($event)"></div>
<!-- rotate events -->
<div (rotate)="logEvent($event)"></div>
<div (rotatestart)="logEvent($event)"></div>
<div (rotatemove)="logEvent($event)"></div>
<div (rotateend)="logEvent($event)"></div>
<div (rotatecancel)="logEvent($event)"></div>
<!-- swipe events -->
<div (swipe)="logEvent($event)"></div>
<div (swipeleft)="logEvent($event)"></div>
<div (swiperight)="logEvent($event)"></div>
<div (swipeup)="logEvent($event)"></div>
<div (swipedown)="logEvent($event)"></div>
<!-- tap event -->
<div (tap)="logEvent($event)"></div>
You can create own helper component and use it instead of *ngIf.
@Component({
selector: 'loader',
template: `
<ng-content *ngIf="!loading else showLoader"></ng-content>
<ng-template #showLoader>🕚 Wait 10 seconds!</ng-template>
`
})
class LoaderComponent {
@Input() loading: boolean;
}
For usage example:
<loader [loading]="isLoading">🦊 🦄 🐉</loader>
Note that the content will be eagerly evaluated, e.g. in the snippet below
destroy-the-worldwill be created before the loading even starts:
<loader [loading]="isLoading"><destroy-the-world></destroy-the-world></loader>
With ng-content you can pass any elements to a component.
This simplifies creating reusable components.
@Component({
selector: 'wrapper',
template: `
<div class="wrapper">
<ng-content></ng-content>
</div>
`,
})
export class Wrapper {}
<wrapper>
<h1>Hello World!</h1>
</wrapper>
*ngIf directive also supports else statement.
<div *ngIf="isLoading; else notLoading">loading...</div>
<ng-template #notLoading>not loading</ng-template>
Navigate with matrix params:
the router will navigate to /first;name=foo/details
<a [routerLink]="['/', 'first', {name: 'foo'}, 'details']">
link with params
</a>
In certain cases @Input and @Output properties can be named differently than the actual inputs and outputs.
<div
pagination
paginationShowFirst="true"
(paginationPageChanged)="onPageChanged($event)">
</div>
@Directive({ selector: '[pagination]'})
class PaginationComponent {
@Input('paginationShowFirst')
showFirst: boolean = true;
@Output('paginationPageChanged')
pageChanged = new EventEmitter();
}
Note: Use this wisely, see StyleGuide recommedation
The Safe Navigation Operator helps with preventing null-reference exceptions in component template expressions. It returns object property value if it exists or null otherwise.
<p> I will work even if student is null or undefined: {{student?.name}} </p>
{{a?.b?.c}}
Underneath will be compiled to.
(_co.a == null)? null: ((_co.a.b == null)? null: _co.a.b.c));
To avoid the expensive operations, we can help Angular to track which items added or removed i.e. customize the default tracking algorithm by providing a trackBy option to NgForOf.
So you can provide your custom trackBy function that will return unique identifier for each iterated item.
For example, some key value of the item. If this key value matches the previous one, then Angular won't detect changes.
trackBy takes a function that has index and item args.
@Component({
selector: 'my-app',
template: `
<ul>
<li *ngFor="let item of items; trackBy: trackByFn">{{item.id}}</li>
</ul>
`
})
export class AppComponent {
trackByFn(index, item) {
return item.id;
}
}
If trackBy is given, Angular tracks changes by the return value of the function.
Now when you change the collection, Angular can track which items have been added or removed according to the unique identifier and create/destroy only changed items.
Under the hood Angular compiles structural directives into ng-template elements, e.g.:
<!-- This -->
<div *ngFor="let item of [1,2,3]">
<!-- Get expanded into this -->
<ng-template ngFor [ngForOf]="[1,2,3]" let-item="$implicit"></ng-template>
The value passed to *ngFor directive is written using microsyntax. You can learn about it in the docs.
Also check out an interactive tool that shows the expansion by Alexey Zuev
It's possible to use @ViewChild (also @ViewChildren and @ContentChild/Children) to query for components of different types using dependency injection.
In the example below we can use @ViewChildren(Base) to get instances of Foo and Bar.
abstract class Base {}
@Component({
selector: 'foo',
providers: [{ provide: Base, useExisting: Foo }]
})
class Foo extends Base {}
@Component({
selector: 'bar',
providers: [{ provide: Base, useExisting: Bar }]
})
class Bar extends Base {}
// Now we can require both types of components using Base.
@Component({ template: `<foo></foo><bar></bar>` })
class AppComponent {
@ViewChildren(Base) components: QueryList<Base>;
}
Angular allows us to control the way module preloading is handled.
There are 2 strategies provided by @angular/router: PreloadAllModules and NoPreloading. The latter enabled by default, only preloading lazy modules on demand.
We can override this behavior by providing custom preloading strategy: In the example below we preload all included modules if the connection is good.
import { Observable, of } from 'rxjs';
export class CustomPreloading implements PreloadingStrategy {
public preload(route: Route, load: () => Observable<any>): Observable<any> {
return preloadingConnection() ? load() : of(null);
}
}
const routing: ModuleWithProviders = RouterModule.forRoot(routes, {
preloadingStrategy: CustomPreloading
});
Note that that the example above would not be very efficient for larger apps, as it'll preload all the modules.
It is possible to use SVG tags in your Angular component, to create beautiful graphs and visualizations. There are 3 things you need to know:
attr<circle [attr.cx]="x" [attr.cy]="y"></circle>
// Not: <child-component></child-component>
<g child-component></g>
@Component({selector: '[child-component]' })
@Component({
selector: '[child-component]',
template: `<svg:circle></svg:circle>`
})