# Cheat Sheet
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.