angular-cn/aio/content/guide/cheatsheet.md

@title Cheat Sheet

@description

Bootstrapping	import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
platformBrowserDynamic().bootstrapModule(AppModule);	Bootstraps the app, using the root component from the specified NgModule.

NgModules	import { NgModule } from '@angular/core';
@NgModule({ declarations: ..., imports: ...,      exports: ..., providers: ..., bootstrap: ...}) class MyModule {}	Defines a module that contains components, directives, pipes, and providers.
declarations: [MyRedComponent, MyBlueComponent, MyDatePipe]	List of components, directives, and pipes that belong to this module.
imports: [BrowserModule, SomeOtherModule]	List of modules to import into this module. Everything from the imported modules is available to declarations of this module.
exports: [MyRedComponent, MyDatePipe]	List of components, directives, and pipes visible to modules that import this module.
providers: [MyService, { provide: ... }]	List of dependency injection providers visible both to the contents of this module and to importers of this module.
bootstrap: [MyAppComponent]	List of components to bootstrap when this module is bootstrapped.

Template syntax
<input [value]="firstName">	Binds property value to the result of expression firstName.
<div [attr.role]="myAriaRole">	Binds attribute role to the result of expression myAriaRole.
<div [class.extra-sparkle]="isDelightful">	Binds the presence of the CSS class extra-sparkle on the element to the truthiness of the expression isDelightful.
<div [style.width.px]="mySize">	Binds style property width to the result of expression mySize in pixels. Units are optional.
<button (click)="readRainbow($event)">	Calls method readRainbow when a click event is triggered on this button element (or its children) and passes in the event object.
<div title="Hello {{ponyName}}">	Binds a property to an interpolated string, for example, "Hello Seabiscuit". Equivalent to: <div [title]="'Hello ' + ponyName">
<p>Hello {{ponyName}}</p>	Binds text content to an interpolated string, for example, "Hello Seabiscuit".
<my-cmp [(title)]="name">	Sets up two-way data binding. Equivalent to: <my-cmp [title]="name" (titleChange)="name=$event">
<video #movieplayer ...>   <button (click)="movieplayer.play()"> </video>	Creates a local variable movieplayer that provides access to the video element instance in data-binding and event-binding expressions in the current template.
<p *myUnless="myExpression">...</p>	The * symbol turns the current element into an embedded template. Equivalent to: <ng-template [myUnless]="myExpression"><p>...</p></ng-template>
<p>Card No.: {{cardNumber | myCardNumberFormatter}}</p>	Transforms the current value of expression cardNumber via the pipe called myCardNumberFormatter.
<p>Employer: {{employer?.companyName}}</p>	The safe navigation operator (?) means that the employer field is optional and if undefined, the rest of the expression should be ignored.
<svg:rect x="0" y="0" width="100" height="100"/>	An SVG snippet template needs an svg: prefix on its root element to disambiguate the SVG element from an HTML component.
<svg>   <rect x="0" y="0" width="100" height="100"/> </svg>	An <svg> root element is detected as an SVG element automatically, without the prefix.

Built-in directives	import { CommonModule } from '@angular/common';
<section *ngIf="showSection">	Removes or recreates a portion of the DOM tree based on the showSection expression.
<li *ngFor="let item of list">	Turns the li element and its contents into a template, and uses that to instantiate a view for each item in list.
<div [ngSwitch]="conditionExpression">   <ng-template [ngSwitchCase]="case1Exp">...</ng-template>   <ng-template ngSwitchCase="case2LiteralString">...</ng-template>   <ng-template ngSwitchDefault>...</ng-template> </div>	Conditionally swaps the contents of the div by selecting one of the embedded templates based on the current value of conditionExpression.
<div [ngClass]="{active: isActive, disabled: isDisabled}">	Binds the presence of CSS classes on the element to the truthiness of the associated map values. The right-hand expression should return {class-name: true/false} map.

Forms	import { FormsModule } from '@angular/forms';
<input [(ngModel)]="userName">	Provides two-way data-binding, parsing, and validation for form controls.

Class decorators	import { Directive, ... } from '@angular/core';
@Component({...}) class MyComponent() {}	Declares that a class is a component and provides metadata about the component.
@Directive({...}) class MyDirective() {}	Declares that a class is a directive and provides metadata about the directive.
@Pipe({...}) class MyPipe() {}	Declares that a class is a pipe and provides metadata about the pipe.
@Injectable() class MyService() {}	Declares that a class has dependencies that should be injected into the constructor when the dependency injector is creating an instance of this class.

Directive configuration	@Directive({ property1: value1, ... })
selector: '.cool-button:not(a)'	Specifies a CSS selector that identifies this directive within a template. Supported selectors include element, [attribute], .class, and :not(). Does not support parent-child relationship selectors.
providers: [MyService, { provide: ... }]	List of dependency injection providers for this directive and its children.

Component configuration	@Component extends @Directive, so the @Directive configuration applies to components as well
moduleId: module.id	If set, the templateUrl and styleUrl are resolved relative to the component.
viewProviders: [MyService, { provide: ... }]	List of dependency injection providers scoped to this component's view.
template: 'Hello {{name}}' templateUrl: 'my-component.html'	Inline template or external template URL of the component's view.
styles: ['.primary {color: red}'] styleUrls: ['my-component.css']	List of inline CSS styles or external stylesheet URLs for styling the component’s view.

Class field decorators for directives and components	import { Input, ... } from '@angular/core';
@Input() myProperty;	Declares an input property that you can update via property binding (example: <my-cmp [myProperty]="someExpression">).
@Output() myEvent = new EventEmitter();	Declares an output property that fires events that you can subscribe to with an event binding (example: <my-cmp (myEvent)="doSomething()">).
@HostBinding('class.valid') isValid;	Binds a host element property (here, the CSS class valid) to a directive/component property (isValid).
@HostListener('click', ['$event']) onClick(e) {...}	Subscribes to a host element event (click) with a directive/component method (onClick), optionally passing an argument ($event).
@ContentChild(myPredicate) myChildComponent;	Binds the first result of the component content query (myPredicate) to a property (myChildComponent) of the class.
@ContentChildren(myPredicate) myChildComponents;	Binds the results of the component content query (myPredicate) to a property (myChildComponents) of the class.
@ViewChild(myPredicate) myChildComponent;	Binds the first result of the component view query (myPredicate) to a property (myChildComponent) of the class. Not available for directives.
@ViewChildren(myPredicate) myChildComponents;	Binds the results of the component view query (myPredicate) to a property (myChildComponents) of the class. Not available for directives.

Directive and component change detection and lifecycle hooks	(implemented as class methods)
constructor(myService: MyService, ...) { ... }	Called before any other lifecycle hook. Use it to inject dependencies, but avoid any serious work here.
ngOnChanges(changeRecord) { ... }	Called after every change to input properties and before processing content or child views.
ngOnInit() { ... }	Called after the constructor, initializing input properties, and the first call to ngOnChanges.
ngDoCheck() { ... }	Called every time that the input properties of a component or a directive are checked. Use it to extend change detection by performing a custom check.
ngAfterContentInit() { ... }	Called after ngOnInit when the component's or directive's content has been initialized.
ngAfterContentChecked() { ... }	Called after every check of the component's or directive's content.
ngAfterViewInit() { ... }	Called after ngAfterContentInit when the component's view has been initialized. Applies to components only.
ngAfterViewChecked() { ... }	Called after every check of the component's view. Applies to components only.
ngOnDestroy() { ... }	Called once, before the instance is destroyed.

Dependency injection configuration
{ provide: MyService, useClass: MyMockService }	Sets or overrides the provider for MyService to the MyMockService class.
{ provide: MyService, useFactory: myFactory }	Sets or overrides the provider for MyService to the myFactory factory function.
{ provide: MyValue, useValue: 41 }	Sets or overrides the provider for MyValue to the value 41.

Routing and navigation	import { Routes, RouterModule, ... } from '@angular/router';
const routes: Routes = [   { path: '', component: HomeComponent },   { path: 'path/:routeParam', component: MyComponent },   { path: 'staticPath', component: ... },   { path: '**', component: ... },   { path: 'oldPath', redirectTo: '/staticPath' },   { path: ..., component: ..., data: { message: 'Custom' } } ]); const routing = RouterModule.forRoot(routes);	Configures routes for the application. Supports static, parameterized, redirect, and wildcard routes. Also supports custom route data and resolve.
<router-outlet></router-outlet> <router-outlet name="aux"></router-outlet>	Marks the location to load the component of the active route.
<a routerLink="/path"> <a [routerLink]="[ '/path', routeParam ]"> <a [routerLink]="[ '/path', { matrixParam: 'value' } ]"> <a [routerLink]="[ '/path' ]" [queryParams]="{ page: 1 }"> <a [routerLink]="[ '/path' ]" fragment="anchor">	Creates a link to a different view based on a route instruction consisting of a route path, required and optional parameters, query parameters, and a fragment. To navigate to a root route, use the / prefix; for a child route, use the ./prefix; for a sibling or parent, use the ../ prefix.
<a [routerLink]="[ '/path' ]" routerLinkActive="active">	The provided classes are added to the element when the routerLink becomes the current active route.
class CanActivateGuard implements CanActivate {     canActivate(       route: ActivatedRouteSnapshot,       state: RouterStateSnapshot     ): Observable<boolean>|Promise<boolean>|boolean { ... } } { path: ..., canActivate: [CanActivateGuard] }	An interface for defining a class that the router should call first to determine if it should activate this component. Should return a boolean or an Observable/Promise that resolves to a boolean.
class CanDeactivateGuard implements CanDeactivate<T> {     canDeactivate(       component: T,       route: ActivatedRouteSnapshot,       state: RouterStateSnapshot     ): Observable<boolean>|Promise<boolean>|boolean { ... } } { path: ..., canDeactivate: [CanDeactivateGuard] }	An interface for defining a class that the router should call first to determine if it should deactivate this component after a navigation. Should return a boolean or an Observable/Promise that resolves to a boolean.
class CanActivateChildGuard implements CanActivateChild {     canActivateChild(       route: ActivatedRouteSnapshot,       state: RouterStateSnapshot     ): Observable<boolean>|Promise<boolean>|boolean { ... } } { path: ..., canActivateChild: [CanActivateGuard],     children: ... }	An interface for defining a class that the router should call first to determine if it should activate the child route. Should return a boolean or an Observable/Promise that resolves to a boolean.
class ResolveGuard implements Resolve<T> {     resolve(       route: ActivatedRouteSnapshot,       state: RouterStateSnapshot     ): Observable<any>|Promise<any>|any { ... } } { path: ..., resolve: [ResolveGuard] }	An interface for defining a class that the router should call first to resolve route data before rendering the route. Should return a value or an Observable/Promise that resolves to a value.
class CanLoadGuard implements CanLoad {     canLoad(       route: Route     ): Observable<boolean>|Promise<boolean>|boolean { ... } } { path: ..., canLoad: [CanLoadGuard], loadChildren: ... }	An interface for defining a class that the router should call first to check if the lazy loaded module should be loaded. Should return a boolean or an Observable/Promise that resolves to a boolean.