angular-cn/modules/@angular/core/src/metadata/directives.ts

/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {AnimationEntryMetadata} from '../animation/metadata';
import {ChangeDetectionStrategy} from '../change_detection/constants';
import {InjectableMetadata} from '../di/metadata';
import {Type, isPresent} from '../facade/lang';

import {ViewEncapsulation} from './view';

/**
 * Interface for creating {@link DirectiveMetadata}
 * @experimental
 */
export interface DirectiveMetadataType {
  selector?: string;
  properties?: string[];
  inputs?: string[];
  events?: string[];
  outputs?: string[];
  host?: {[key: string]: string};
  providers?: any[];
  exportAs?: string;
  queries?: {[key: string]: any};
}

/**
 * Directives allow you to attach behavior to elements in the DOM.
 *
 * {@link DirectiveMetadata}s with an embedded view are called {@link ComponentMetadata}s.
 *
 * A directive consists of a single directive annotation and a controller class. When the
 * directive's `selector` matches
 * elements in the DOM, the following steps occur:
 *
 * 1. For each directive, the `ElementInjector` attempts to resolve the directive's constructor
 * arguments.
 * 2. Angular instantiates directives for each matched element using `ElementInjector` in a
 * depth-first order,
 *    as declared in the HTML.
 *
 * ## Understanding How Injection Works
 *
 * There are three stages of injection resolution.
 * - *Pre-existing Injectors*:
 *   - The terminal {@link Injector} cannot resolve dependencies. It either throws an error or, if
 * the dependency was
 *     specified as `@Optional`, returns `null`.
 *   - The platform injector resolves browser singleton resources, such as: cookies, title,
 * location, and others.
 * - *Component Injectors*: Each component instance has its own {@link Injector}, and they follow
 * the same parent-child hierarchy
 *     as the component instances in the DOM.
 * - *Element Injectors*: Each component instance has a Shadow DOM. Within the Shadow DOM each
 * element has an `ElementInjector`
 *     which follow the same parent-child hierarchy as the DOM elements themselves.
 *
 * When a template is instantiated, it also must instantiate the corresponding directives in a
 * depth-first order. The
 * current `ElementInjector` resolves the constructor dependencies for each directive.
 *
 * Angular then resolves dependencies as follows, according to the order in which they appear in the
 * {@link ComponentMetadata}:
 *
 * 1. Dependencies on the current element
 * 2. Dependencies on element injectors and their parents until it encounters a Shadow DOM boundary
 * 3. Dependencies on component injectors and their parents until it encounters the root component
 * 4. Dependencies on pre-existing injectors
 *
 *
 * The `ElementInjector` can inject other directives, element-specific special objects, or it can
 * delegate to the parent
 * injector.
 *
 * To inject other directives, declare the constructor parameter as:
 * - `directive:DirectiveType`: a directive on the current element only
 * - `@Host() directive:DirectiveType`: any directive that matches the type between the current
 * element and the
 *    Shadow DOM root.
 * - `@Query(DirectiveType) query:QueryList<DirectiveType>`: A live collection of direct child
 * directives.
 * - `@QueryDescendants(DirectiveType) query:QueryList<DirectiveType>`: A live collection of any
 * child directives.
 *
 * To inject element-specific special objects, declare the constructor parameter as:
 * - `element: ElementRef` to obtain a reference to logical element in the view.
 * - `viewContainer: ViewContainerRef` to control child template instantiation, for
 * {@link DirectiveMetadata} directives only
 * - `bindingPropagation: BindingPropagation` to control change detection in a more granular way.
 *
 * ### Example
 *
 * The following example demonstrates how dependency injection resolves constructor arguments in
 * practice.
 *
 *
 * Assume this HTML template:
 *
 * ```
 * <div dependency="1">
 *   <div dependency="2">
 *     <div dependency="3" my-directive>
 *       <div dependency="4">
 *         <div dependency="5"></div>
 *       </div>
 *       <div dependency="6"></div>
 *     </div>
 *   </div>
 * </div>
 * ```
 *
 * With the following `dependency` decorator and `SomeService` injectable class.
 *
 * ```
 * @Injectable()
 * class SomeService {
 * }
 *
 * @Directive({
 *   selector: '[dependency]',
 *   inputs: [
 *     'id: dependency'
 *   ]
 * })
 * class Dependency {
 *   id:string;
 * }
 * ```
 *
 * Let's step through the different ways in which `MyDirective` could be declared...
 *
 *
 * ### No injection
 *
 * Here the constructor is declared with no arguments, therefore nothing is injected into
 * `MyDirective`.
 *
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor() {
 *   }
 * }
 * ```
 *
 * This directive would be instantiated with no dependencies.
 *
 *
 * ### Component-level injection
 *
 * Directives can inject any injectable instance from the closest component injector or any of its
 * parents.
 *
 * Here, the constructor declares a parameter, `someService`, and injects the `SomeService` type
 * from the parent
 * component's injector.
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor(someService: SomeService) {
 *   }
 * }
 * ```
 *
 * This directive would be instantiated with a dependency on `SomeService`.
 *
 *
 * ### Injecting a directive from the current element
 *
 * Directives can inject other directives declared on the current element.
 *
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor(dependency: Dependency) {
 *     expect(dependency.id).toEqual(3);
 *   }
 * }
 * ```
 * This directive would be instantiated with `Dependency` declared at the same element, in this case
 * `dependency="3"`.
 *
 * ### Injecting a directive from any ancestor elements
 *
 * Directives can inject other directives declared on any ancestor element (in the current Shadow
 * DOM), i.e. on the current element, the
 * parent element, or its parents.
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor(@Host() dependency: Dependency) {
 *     expect(dependency.id).toEqual(2);
 *   }
 * }
 * ```
 *
 * `@Host` checks the current element, the parent, as well as its parents recursively. If
 * `dependency="2"` didn't
 * exist on the direct parent, this injection would
 * have returned
 * `dependency="1"`.
 *
 *
 * ### Injecting a live collection of direct child directives
 *
 *
 * A directive can also query for other child directives. Since parent directives are instantiated
 * before child directives, a directive can't simply inject the list of child directives. Instead,
 * the directive injects a {@link QueryList}, which updates its contents as children are added,
 * removed, or moved by a directive that uses a {@link ViewContainerRef} such as a `ngFor`, an
 * `ngIf`, or an `ngSwitch`.
 *
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor(@Query(Dependency) dependencies:QueryList<Dependency>) {
 *   }
 * }
 * ```
 *
 * This directive would be instantiated with a {@link QueryList} which contains `Dependency` 4 and
 * `Dependency` 6. Here, `Dependency` 5 would not be included, because it is not a direct child.
 *
 * ### Injecting a live collection of descendant directives
 *
 * By passing the descendant flag to `@Query` above, we can include the children of the child
 * elements.
 *
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor(@Query(Dependency, {descendants: true}) dependencies:QueryList<Dependency>) {
 *   }
 * }
 * ```
 *
 * This directive would be instantiated with a Query which would contain `Dependency` 4, 5 and 6.
 *
 * ### Optional injection
 *
 * The normal behavior of directives is to return an error when a specified dependency cannot be
 * resolved. If you
 * would like to inject `null` on unresolved dependency instead, you can annotate that dependency
 * with `@Optional()`.
 * This explicitly permits the author of a template to treat some of the surrounding directives as
 * optional.
 *
 * ```
 * @Directive({ selector: '[my-directive]' })
 * class MyDirective {
 *   constructor(@Optional() dependency:Dependency) {
 *   }
 * }
 * ```
 *
 * This directive would be instantiated with a `Dependency` directive found on the current element.
 * If none can be
 * found, the injector supplies `null` instead of throwing an error.
 *
 * ### Example
 *
 * Here we use a decorator directive to simply define basic tool-tip behavior.
 *
 * ```
 * @Directive({
 *   selector: '[tooltip]',
 *   inputs: [
 *     'text: tooltip'
 *   ],
 *   host: {
 *     '(mouseenter)': 'onMouseEnter()',
 *     '(mouseleave)': 'onMouseLeave()'
 *   }
 * })
 * class Tooltip{
 *   text:string;
 *   overlay:Overlay; // NOT YET IMPLEMENTED
 *   overlayManager:OverlayManager; // NOT YET IMPLEMENTED
 *
 *   constructor(overlayManager:OverlayManager) {
 *     this.overlay = overlay;
 *   }
 *
 *   onMouseEnter() {
 *     // exact signature to be determined
 *     this.overlay = this.overlayManager.open(text, ...);
 *   }
 *
 *   onMouseLeave() {
 *     this.overlay.close();
 *     this.overlay = null;
 *   }
 * }
 * ```
 * In our HTML template, we can then add this behavior to a `<div>` or any other element with the
 * `tooltip` selector,
 * like so:
 *
 * ```
 * <div tooltip="some text here"></div>
 * ```
 *
 * Directives can also control the instantiation, destruction, and positioning of inline template
 * elements:
 *
 * A directive uses a {@link ViewContainerRef} to instantiate, insert, move, and destroy views at
 * runtime.
 * The {@link ViewContainerRef} is created as a result of `<template>` element, and represents a
 * location in the current view
 * where these actions are performed.
 *
 * Views are always created as children of the current {@link ComponentMetadata}, and as siblings of
 * the
 * `<template>` element. Thus a
 * directive in a child view cannot inject the directive that created it.
 *
 * Since directives that create views via ViewContainers are common in Angular, and using the full
 * `<template>` element syntax is wordy, Angular
 * also supports a shorthand notation: `<li *foo="bar">` and `<li template="foo: bar">` are
 * equivalent.
 *
 * Thus,
 *
 * ```
 * <ul>
 *   <li *foo="bar" title="text"></li>
 * </ul>
 * ```
 *
 * Expands in use to:
 *
 * ```
 * <ul>
 *   <template [foo]="bar">
 *     <li title="text"></li>
 *   </template>
 * </ul>
 * ```
 *
 * Notice that although the shorthand places `*foo="bar"` within the `<li>` element, the binding for
 * the directive
 * controller is correctly instantiated on the `<template>` element rather than the `<li>` element.
 *
 * ## Lifecycle hooks
 *
 * When the directive class implements some {@linkDocs guide/lifecycle-hooks} the
 * callbacks are called by the change detection at defined points in time during the life of the
 * directive.
 *
 * ### Example
 *
 * Let's suppose we want to implement the `unless` behavior, to conditionally include a template.
 *
 * Here is a simple directive that triggers on an `unless` selector:
 *
 * ```
 * @Directive({
 *   selector: '[unless]',
 *   inputs: ['unless']
 * })
 * export class Unless {
 *   viewContainer: ViewContainerRef;
 *   templateRef: TemplateRef;
 *   prevCondition: boolean;
 *
 *   constructor(viewContainer: ViewContainerRef, templateRef: TemplateRef) {
 *     this.viewContainer = viewContainer;
 *     this.templateRef = templateRef;
 *     this.prevCondition = null;
 *   }
 *
 *   set unless(newCondition) {
 *     if (newCondition && (isBlank(this.prevCondition) || !this.prevCondition)) {
 *       this.prevCondition = true;
 *       this.viewContainer.clear();
 *     } else if (!newCondition && (isBlank(this.prevCondition) || this.prevCondition)) {
 *       this.prevCondition = false;
 *       this.viewContainer.create(this.templateRef);
 *     }
 *   }
 * }
 * ```
 *
 * We can then use this `unless` selector in a template:
 * ```
 * <ul>
 *   <li *unless="expr"></li>
 * </ul>
 * ```
 *
 * Once the directive instantiates the child view, the shorthand notation for the template expands
 * and the result is:
 *
 * ```
 * <ul>
 *   <template [unless]="exp">
 *     <li></li>
 *   </template>
 *   <li></li>
 * </ul>
 * ```
 *
 * Note also that although the `<li></li>` template still exists inside the `<template></template>`,
 * the instantiated
 * view occurs on the second `<li></li>` which is a sibling to the `<template>` element.
 * @stable
 */
export class DirectiveMetadata extends InjectableMetadata implements DirectiveMetadataType {
  /**
   * The CSS selector that triggers the instantiation of a directive.
   *
   * Angular only allows directives to trigger on CSS selectors that do not cross element
   * boundaries.
   *
   * `selector` may be declared as one of the following:
   *
   * - `element-name`: select by element name.
   * - `.class`: select by class name.
   * - `[attribute]`: select by attribute name.
   * - `[attribute=value]`: select by attribute name and value.
   * - `:not(sub_selector)`: select only if the element does not match the `sub_selector`.
   * - `selector1, selector2`: select if either `selector1` or `selector2` matches.
   *
   *
   * ### Example
   *
   * Suppose we have a directive with an `input[type=text]` selector.
   *
   * And the following HTML:
   *
   * ```html
   * <form>
   *   <input type="text">
   *   <input type="radio">
   * <form>
   * ```
   *
   * The directive would only be instantiated on the `<input type="text">` element.
   *
   */
  selector: string;

  /**
   * Enumerates the set of data-bound input properties for a directive
   *
   * Angular automatically updates input properties during change detection.
   *
   * The `inputs` property defines a set of `directiveProperty` to `bindingProperty`
   * configuration:
   *
   * - `directiveProperty` specifies the component property where the value is written.
   * - `bindingProperty` specifies the DOM property where the value is read from.
   *
   * When `bindingProperty` is not provided, it is assumed to be equal to `directiveProperty`.
   *
   * ### Example ([live demo](http://plnkr.co/edit/ivhfXY?p=preview))
   *
   * The following example creates a component with two data-bound properties.
   *
   * ```typescript
   * @Component({
   *   selector: 'bank-account',
   *   inputs: ['bankName', 'id: account-id'],
   *   template: `
   *     Bank Name: {{bankName}}
   *     Account Id: {{id}}
   *   `
   * })
   * class BankAccount {
   *   bankName: string;
   *   id: string;
   *
   *   // this property is not bound, and won't be automatically updated by Angular
   *   normalizedBankName: string;
   * }
   *
   * @Component({
   *   selector: 'app',
   *   template: `
   *     <bank-account bank-name="RBC" account-id="4747"></bank-account>
   *   `,
   *   directives: [BankAccount]
   * })
   * class App {}
   *
   * bootstrap(App);
   * ```
   *
   */
  get inputs(): string[] {
    return isPresent(this._properties) && this._properties.length > 0 ? this._properties :
                                                                        this._inputs;
  }
  /**
   * Use `inputs` instead
   *
   * @deprecated
   */
  get properties(): string[] { return this.inputs; }
  private _inputs: string[];
  private _properties: string[];

  /**
   * Enumerates the set of event-bound output properties.
   *
   * When an output property emits an event, an event handler attached to that event
   * the template is invoked.
   *
   * The `outputs` property defines a set of `directiveProperty` to `bindingProperty`
   * configuration:
   *
   * - `directiveProperty` specifies the component property that emits events.
   * - `bindingProperty` specifies the DOM property the event handler is attached to.
   *
   * ### Example ([live demo](http://plnkr.co/edit/d5CNq7?p=preview))
   *
   * ```typescript
   * @Directive({
   *   selector: 'interval-dir',
   *   outputs: ['everySecond', 'five5Secs: everyFiveSeconds']
   * })
   * class IntervalDir {
   *   everySecond = new EventEmitter();
   *   five5Secs = new EventEmitter();
   *
   *   constructor() {
   *     setInterval(() => this.everySecond.emit("event"), 1000);
   *     setInterval(() => this.five5Secs.emit("event"), 5000);
   *   }
   * }
   *
   * @Component({
   *   selector: 'app',
   *   template: `
   *     <interval-dir (everySecond)="everySecond()" (everyFiveSeconds)="everyFiveSeconds()">
   *     </interval-dir>
   *   `,
   *   directives: [IntervalDir]
   * })
   * class App {
   *   everySecond() { console.log('second'); }
   *   everyFiveSeconds() { console.log('five seconds'); }
   * }
   * bootstrap(App);
   * ```
   *
   */
  get outputs(): string[] {
    return isPresent(this._events) && this._events.length > 0 ? this._events : this._outputs;
  }
  /**
   * Use `outputs` instead
   *
   * @deprecated
   */
  get events(): string[] { return this.outputs; }
  private _outputs: string[];
  private _events: string[];

  /**
   * Specify the events, actions, properties and attributes related to the host element.
   *
   * ## Host Listeners
   *
   * Specifies which DOM events a directive listens to via a set of `(event)` to `method`
   * key-value pairs:
   *
   * - `event`: the DOM event that the directive listens to.
   * - `statement`: the statement to execute when the event occurs.
   * If the evaluation of the statement returns `false`, then `preventDefault`is applied on the DOM
   * event.
   *
   * To listen to global events, a target must be added to the event name.
   * The target can be `window`, `document` or `body`.
   *
   * When writing a directive event binding, you can also refer to the $event local variable.
   *
   * ### Example ([live demo](http://plnkr.co/edit/DlA5KU?p=preview))
   *
   * The following example declares a directive that attaches a click listener to the button and
   * counts clicks.
   *
   * ```typescript
   * @Directive({
   *   selector: 'button[counting]',
   *   host: {
   *     '(click)': 'onClick($event.target)'
   *   }
   * })
   * class CountClicks {
   *   numberOfClicks = 0;
   *
   *   onClick(btn) {
   *     console.log("button", btn, "number of clicks:", this.numberOfClicks++);
   *   }
   * }
   *
   * @Component({
   *   selector: 'app',
   *   template: `<button counting>Increment</button>`,
   *   directives: [CountClicks]
   * })
   * class App {}
   *
   * bootstrap(App);
   * ```
   *
   * ## Host Property Bindings
   *
   * Specifies which DOM properties a directive updates.
   *
   * Angular automatically checks host property bindings during change detection.
   * If a binding changes, it will update the host element of the directive.
   *
   * ### Example ([live demo](http://plnkr.co/edit/gNg0ED?p=preview))
   *
   * The following example creates a directive that sets the `valid` and `invalid` classes
   * on the DOM element that has ngModel directive on it.
   *
   * ```typescript
   * @Directive({
   *   selector: '[ngModel]',
   *   host: {
   *     '[class.valid]': 'valid',
   *     '[class.invalid]': 'invalid'
   *   }
   * })
   * class NgModelStatus {
   *   constructor(public control:NgModel) {}
   *   get valid { return this.control.valid; }
   *   get invalid { return this.control.invalid; }
   * }
   *
   * @Component({
   *   selector: 'app',
   *   template: `<input [(ngModel)]="prop">`,
   *   directives: [FORM_DIRECTIVES, NgModelStatus]
   * })
   * class App {
   *   prop;
   * }
   *
   * bootstrap(App);
   * ```
   *
   * ## Attributes
   *
   * Specifies static attributes that should be propagated to a host element.
   *
   * ### Example
   *
   * In this example using `my-button` directive (ex.: `<div my-button></div>`) on a host element
   * (here: `<div>` ) will ensure that this element will get the "button" role.
   *
   * ```typescript
   * @Directive({
   *   selector: '[my-button]',
   *   host: {
   *     'role': 'button'
   *   }
   * })
   * class MyButton {
   * }
   * ```
   */
  host: {[key: string]: string};

  /**
   * Defines the set of injectable objects that are visible to a Directive and its light DOM
   * children.
   *
   * ## Simple Example
   *
   * Here is an example of a class that can be injected:
   *
   * ```
   * class Greeter {
   *    greet(name:string) {
   *      return 'Hello ' + name + '!';
   *    }
   * }
   *
   * @Directive({
   *   selector: 'greet',
   *   providers: [
   *     Greeter
   *   ]
   * })
   * class HelloWorld {
   *   greeter:Greeter;
   *
   *   constructor(greeter:Greeter) {
   *     this.greeter = greeter;
   *   }
   * }
   * ```
   */
  get providers(): any[] { return this._providers; }
  private _providers: any[];

  /**
   * Defines the name that can be used in the template to assign this directive to a variable.
   *
   * ## Simple Example
   *
   * ```
   * @Directive({
   *   selector: 'child-dir',
   *   exportAs: 'child'
   * })
   * class ChildDir {
   * }
   *
   * @Component({
   *   selector: 'main',
   *   template: `<child-dir #c="child"></child-dir>`,
   *   directives: [ChildDir]
   * })
   * class MainComponent {
   * }
   *
   * ```
   */
  exportAs: string;

  // TODO: add an example after ContentChildren and ViewChildren are in master
  /**
   * Configures the queries that will be injected into the directive.
   *
   * Content queries are set before the `ngAfterContentInit` callback is called.
   * View queries are set before the `ngAfterViewInit` callback is called.
   *
   * ### Example
   *
   * ```
   * @Component({
   *   selector: 'someDir',
   *   queries: {
   *     contentChildren: new ContentChildren(ChildDirective),
   *     viewChildren: new ViewChildren(ChildDirective)
   *   },
   *   template: '<child-directive></child-directive>',
   *   directives: [ChildDirective]
   * })
   * class SomeDir {
   *   contentChildren: QueryList<ChildDirective>,
   *   viewChildren: QueryList<ChildDirective>
   *
   *   ngAfterContentInit() {
   *     // contentChildren is set
   *   }
   *
   *   ngAfterViewInit() {
   *     // viewChildren is set
   *   }
   * }
   * ```
   */
  queries: {[key: string]: any};

  constructor(
      {selector, inputs, outputs, properties, events, host, providers, exportAs,
       queries}: DirectiveMetadataType = {}) {
    super();
    this.selector = selector;
    this._inputs = inputs;
    this._properties = properties;
    this._outputs = outputs;
    this._events = events;
    this.host = host;
    this.exportAs = exportAs;
    this.queries = queries;
    this._providers = providers;
  }
}

/**
 * Interface for creating {@link ComponentMetadataType}
 * @experimental
 */
export interface ComponentMetadataType extends DirectiveMetadataType {
  changeDetection?: ChangeDetectionStrategy;
  viewProviders?: any[];
  moduleId?: string;
  templateUrl?: string;
  template?: string;
  styleUrls?: string[];
  styles?: string[];
  animations?: AnimationEntryMetadata[];
  directives?: Array<Type|any[]>;
  pipes?: Array<Type|any[]>;
  encapsulation?: ViewEncapsulation;
  interpolation?: [string, string];
  entryComponents?: Array<Type|any[]>;
}

/**
 * Declare reusable UI building blocks for an application.
 *
 * Each Angular component requires a single `@Component` annotation. The
 * `@Component`
 * annotation specifies when a component is instantiated, and which properties and hostListeners it
 * binds to.
 *
 * When a component is instantiated, Angular
 * - creates a shadow DOM for the component.
 * - loads the selected template into the shadow DOM.
 * - creates all the injectable objects configured with `providers` and `viewProviders`.
 *
 * All template expressions and statements are then evaluated against the component instance.
 *
 * ## Lifecycle hooks
 *
 * When the component class implements some {@linkDocs guide/lifecycle-hooks} the
 * callbacks are called by the change detection at defined points in time during the life of the
 * component.
 *
 * ### Example
 *
 * {@example core/ts/metadata/metadata.ts region='component'}
 * @stable
 */
export class ComponentMetadata extends DirectiveMetadata implements ComponentMetadataType {
  /**
   * Defines the used change detection strategy.
   *
   * When a component is instantiated, Angular creates a change detector, which is responsible for
   * propagating the component's bindings.
   *
   * The `changeDetection` property defines, whether the change detection will be checked every time
   * or only when the component tells it to do so.
   */
  changeDetection: ChangeDetectionStrategy;

  /**
   * Defines the set of injectable objects that are visible to its view DOM children.
   *
   * ## Simple Example
   *
   * Here is an example of a class that can be injected:
   *
   * ```
   * class Greeter {
   *    greet(name:string) {
   *      return 'Hello ' + name + '!';
   *    }
   * }
   *
   * @Directive({
   *   selector: 'needs-greeter'
   * })
   * class NeedsGreeter {
   *   greeter:Greeter;
   *
   *   constructor(greeter:Greeter) {
   *     this.greeter = greeter;
   *   }
   * }
   *
   * @Component({
   *   selector: 'greet',
   *   viewProviders: [
   *     Greeter
   *   ],
   *   template: `<needs-greeter></needs-greeter>`,
   *   directives: [NeedsGreeter]
   * })
   * class HelloWorld {
   * }
   *
   * ```
   */
  get viewProviders(): any[] { return this._viewProviders; }
  private _viewProviders: any[];

  /**
   * The module id of the module that contains the component.
   * Needed to be able to resolve relative urls for templates and styles.
   * In CommonJS, this can always be set to `module.id`, similarly SystemJS exposes `__moduleName`
   * variable within each module.
   *
   *
   * ## Simple Example
   *
   * ```
   * @Directive({
   *   selector: 'someDir',
   *   moduleId: module.id
   * })
   * class SomeDir {
   * }
   *
   * ```
   */
  moduleId: string;

  /**
   * Specifies a template URL for an Angular component.
   *
   * NOTE: Only one of `templateUrl` or `template` can be defined per View.
   *
   * <!-- TODO: what's the url relative to? -->
   */
  templateUrl: string;

  /**
   * Specifies an inline template for an Angular component.
   *
   * NOTE: Only one of `templateUrl` or `template` can be defined per View.
   */
  template: string;

  /**
   * Specifies stylesheet URLs for an Angular component.
   *
   * <!-- TODO: what's the url relative to? -->
   */
  styleUrls: string[];

  /**
   * Specifies an inline stylesheet for an Angular component.
   */
  styles: string[];

  /**
   * Animations are defined on components via an animation-like DSL. This DSL approach to describing
   * animations allows for a flexibility that both benefits developers and the framework.
   *
   * Animations work by listening on state changes that occur on an element within
   * the template. When a state change occurs, Angular can then take advantage and animate the
   * arc in between. This works similar to how CSS transitions work, however, by having a
   * programmatic DSL, animations are not limited to environments that are DOM-specific.
   * (Angular can also perform optimizations behind the scenes to make animations more performant.)
   *
   * For animations to be available for use, animation state changes are placed within
   * {@link trigger animation triggers} which are housed inside of the `animations` annotation
   * metadata. Within a trigger both {@link state state} and {@link transition transition} entries
   * can be placed.
   *
   * ```typescript
   * @Component({
   *   selector: 'animation-cmp',
   *   templateUrl: 'animation-cmp.html',
   *   animations: [
   *     // this here is our animation trigger that
   *     // will contain our state change animations.
   *     trigger('myTriggerName', [
   *       // the styles defined for the `on` and `off`
   *       // states declared below are persisted on the
   *       // element once the animation completes.
   *       state('on', style({ opacity: 1 }),
   *       state('off', style({ opacity: 0 }),
   *
   *       // this here is our animation that kicks off when
   *       // this state change jump is true
   *       transition('on => off', [
   *         animate("1s")
   *       ])
   *     ])
   *   ]
   * })
   * ```
   *
   * As depicted in the code above, a group of related animation states are all contained within
   * an animation `trigger` (the code example above called the trigger `myTriggerName`).
   * When a trigger is created then it can be bound onto an element within the component's
   * template via a property prefixed by an `@` symbol followed by trigger name and an expression
   * that
   * is used to determine the state value for that trigger.
   *
   * ```html
   * <!-- animation-cmp.html -->
   * <div @myTriggerName="expression">...</div>
   * ```
   *
   * For state changes to be executed, the `expression` value must change value from its existing
   * value
   * to something that we have set an animation to animate on (in the example above we are listening
   * to a change of state between `on` and `off`). The `expression` value attached to the trigger
   * must be something that can be evaluated with the template/component context.
   *
   * ### DSL Animation Functions
   *
   * Please visit each of the animation DSL functions listed below to gain a better understanding
   * of how and why they are used for crafting animations in Angular2:
   *
   * - {@link trigger trigger()}
   * - {@link state state()}
   * - {@link transition transition()}
   * - {@link group group()}
   * - {@link sequence sequence()}
   * - {@link style style()}
   * - {@link animate animate()}
   * - {@link keyframes keyframes()}
   */
  animations: AnimationEntryMetadata[];

  directives: Array<Type|any[]>;

  pipes: Array<Type|any[]>;

  /**
   * Specify how the template and the styles should be encapsulated.
   * The default is {@link ViewEncapsulation#Emulated `ViewEncapsulation.Emulated`} if the view
   * has styles,
   * otherwise {@link ViewEncapsulation#None `ViewEncapsulation.None`}.
   */
  encapsulation: ViewEncapsulation;

  interpolation: [string, string];

  /**
   * Defines the components that should be compiled as well when
   * this component is defined. For each components listed here,
   * Angular will create a {@link ComponentFactory ComponentFactory} and store it in the
   * {@link ComponentFactoryResolver ComponentFactoryResolver}.
   */
  entryComponents: Array<Type|any[]>;

  constructor({selector,
               inputs,
               outputs,
               properties,
               events,
               host,
               exportAs,
               moduleId,
               providers,
               viewProviders,
               changeDetection = ChangeDetectionStrategy.Default,
               queries,
               templateUrl,
               template,
               styleUrls,
               styles,
               animations,
               directives,
               pipes,
               encapsulation,
               interpolation,
               entryComponents}: ComponentMetadataType = {}) {
    super({
      selector: selector,
      inputs: inputs,
      outputs: outputs,
      properties: properties,
      events: events,
      host: host,
      exportAs: exportAs,
      providers: providers,
      queries: queries
    });

    this.changeDetection = changeDetection;
    this._viewProviders = viewProviders;
    this.templateUrl = templateUrl;
    this.template = template;
    this.styleUrls = styleUrls;
    this.styles = styles;
    this.directives = directives;
    this.pipes = pipes;
    this.encapsulation = encapsulation;
    this.moduleId = moduleId;
    this.animations = animations;
    this.interpolation = interpolation;
    this.entryComponents = entryComponents;
  }
}

/**
 * Interface for creating {@link PipeMetadata}
 * @experimental
 */
export interface PipeMetadataType {
  name: string;
  pure?: boolean;
}

/**
 * Declare reusable pipe function.
 *
 * A "pure" pipe is only re-evaluated when either the input or any of the arguments change.
 *
 * When not specified, pipes default to being pure.
 *
 * ### Example
 *
 * {@example core/ts/metadata/metadata.ts region='pipe'}
 * @stable
 */
export class PipeMetadata extends InjectableMetadata implements PipeMetadataType {
  name: string;
  /** @internal */
  _pure: boolean;

  constructor({name, pure}: PipeMetadataType) {
    super();
    this.name = name;
    this._pure = pure;
  }

  get pure(): boolean { return isPresent(this._pure) ? this._pure : true; }
}

/**
 * Declares a data-bound input property.
 *
 * Angular automatically updates data-bound properties during change detection.
 *
 * `InputMetadata` takes an optional parameter that specifies the name
 * used when instantiating a component in the template. When not provided,
 * the name of the decorated property is used.
 *
 * ### Example
 *
 * The following example creates a component with two input properties.
 *
 * ```typescript
 * @Component({
 *   selector: 'bank-account',
 *   template: `
 *     Bank Name: {{bankName}}
 *     Account Id: {{id}}
 *   `
 * })
 * class BankAccount {
 *   @Input() bankName: string;
 *   @Input('account-id') id: string;
 *
 *   // this property is not bound, and won't be automatically updated by Angular
 *   normalizedBankName: string;
 * }
 *
 * @Component({
 *   selector: 'app',
 *   template: `
 *     <bank-account bank-name="RBC" account-id="4747"></bank-account>
 *   `,
 *   directives: [BankAccount]
 * })
 * class App {}
 *
 * bootstrap(App);
 * ```
 * @stable
 */
export class InputMetadata {
  constructor(
      /**
       * Name used when instantiating a component in the template.
       */
      public bindingPropertyName?: string) {}
}

/**
 * Declares an event-bound output property.
 *
 * When an output property emits an event, an event handler attached to that event
 * the template is invoked.
 *
 * `OutputMetadata` takes an optional parameter that specifies the name
 * used when instantiating a component in the template. When not provided,
 * the name of the decorated property is used.
 *
 * ### Example
 *
 * ```typescript
 * @Directive({
 *   selector: 'interval-dir',
 * })
 * class IntervalDir {
 *   @Output() everySecond = new EventEmitter();
 *   @Output('everyFiveSeconds') five5Secs = new EventEmitter();
 *
 *   constructor() {
 *     setInterval(() => this.everySecond.emit("event"), 1000);
 *     setInterval(() => this.five5Secs.emit("event"), 5000);
 *   }
 * }
 *
 * @Component({
 *   selector: 'app',
 *   template: `
 *     <interval-dir (everySecond)="everySecond()" (everyFiveSeconds)="everyFiveSeconds()">
 *     </interval-dir>
 *   `,
 *   directives: [IntervalDir]
 * })
 * class App {
 *   everySecond() { console.log('second'); }
 *   everyFiveSeconds() { console.log('five seconds'); }
 * }
 * bootstrap(App);
 * ```
 * @stable
 */
export class OutputMetadata {
  constructor(public bindingPropertyName?: string) {}
}

/**
 * Declares a host property binding.
 *
 * Angular automatically checks host property bindings during change detection.
 * If a binding changes, it will update the host element of the directive.
 *
 * `HostBindingMetadata` takes an optional parameter that specifies the property
 * name of the host element that will be updated. When not provided,
 * the class property name is used.
 *
 * ### Example
 *
 * The following example creates a directive that sets the `valid` and `invalid` classes
 * on the DOM element that has ngModel directive on it.
 *
 * ```typescript
 * @Directive({selector: '[ngModel]'})
 * class NgModelStatus {
 *   constructor(public control:NgModel) {}
 *   @HostBinding('class.valid') get valid { return this.control.valid; }
 *   @HostBinding('class.invalid') get invalid { return this.control.invalid; }
 * }
 *
 * @Component({
 *   selector: 'app',
 *   template: `<input [(ngModel)]="prop">`,
 *   directives: [FORM_DIRECTIVES, NgModelStatus]
 * })
 * class App {
 *   prop;
 * }
 *
 * bootstrap(App);
 * ```
 * @stable
 */
export class HostBindingMetadata {
  constructor(public hostPropertyName?: string) {}
}

/**
 * Declares a host listener.
 *
 * Angular will invoke the decorated method when the host element emits the specified event.
 *
 * If the decorated method returns `false`, then `preventDefault` is applied on the DOM
 * event.
 *
 * ### Example
 *
 * The following example declares a directive that attaches a click listener to the button and
 * counts clicks.
 *
 * ```typescript
 * @Directive({selector: 'button[counting]'})
 * class CountClicks {
 *   numberOfClicks = 0;
 *
 *   @HostListener('click', ['$event.target'])
 *   onClick(btn) {
 *     console.log("button", btn, "number of clicks:", this.numberOfClicks++);
 *   }
 * }
 *
 * @Component({
 *   selector: 'app',
 *   template: `<button counting>Increment</button>`,
 *   directives: [CountClicks]
 * })
 * class App {}
 *
 * bootstrap(App);
 * ```
 * @stable
 */
export class HostListenerMetadata {
  constructor(public eventName: string, public args?: string[]) {}
}