Decorator that marks a class as an Angular component and provides configuration metadata that determines how the component should be processed, instantiated, and used at runtime.

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Option	Description
changeDetection?	The change-detection strategy to use for this component.
viewProviders?	Defines the set of injectable objects that are visible to its view DOM children. See example.
moduleId?	The module ID of the module that contains the component. The component must be able to resolve relative URLs for templates and styles. SystemJS exposes the __moduleName variable within each module. In CommonJS, this can be set to module.id.
templateUrl?	The relative path or absolute URL of a template file for an Angular component. If provided, do not supply an inline template using template.
template?	An inline template for an Angular component. If provided, do not supply a template file using templateUrl.
styleUrls?	One or more relative paths or absolute URLs for files containing CSS stylesheets to use in this component.
styles?	One or more inline CSS stylesheets to use in this component.
animations?	One or more animation trigger() calls, containing state() and transition() definitions. See the Animations guide and animations API documentation.
encapsulation?	An encapsulation policy for the component's styling. Possible values: ViewEncapsulation.Emulated: Apply modified component styles in order to emulate a native Shadow DOM CSS encapsulation behavior. ViewEncapsulation.None: Apply component styles globally without any sort of encapsulation. ViewEncapsulation.ShadowDom: Use the browser's native Shadow DOM API to encapsulate styles.
interpolation?	Overrides the default interpolation start and end delimiters ({{ and }}).
preserveWhitespaces?	True to preserve or false to remove potentially superfluous whitespace characters from the compiled template. Whitespace characters are those matching the \s character class in JavaScript regular expressions. Default is false, unless overridden in compiler options.
standalone?	Angular components marked as standalone do not need to be declared in an NgModule. Such components directly manage their own template dependencies (components, directives, and pipes used in a template) via the imports property.
signals?	// TODO(signals): Remove internal and add public documentation.
imports?	The imports property specifies the standalone component's template dependencies — those directives, components, and pipes that can be used within its template. Standalone components can import other standalone components, directives, and pipes as well as existing NgModules.
schemas?	The set of schemas that declare elements to be allowed in a standalone component. Elements and properties that are neither Angular components nor directives must be declared in a schema.

Inherited from Directive decorator

Option	Description
selector?	The CSS selector that identifies this directive in a template and triggers instantiation of the directive.
inputs?	Enumerates the set of data-bound input properties for a directive
outputs?	Enumerates the set of event-bound output properties.
providers?	Configures the injector of this directive or component with a token that maps to a provider of a dependency.
exportAs?	Defines the name that can be used in the template to assign this directive to a variable.
queries?	Configures the queries that will be injected into the directive.
host?	Maps class properties to host element bindings for properties, attributes, and events, using a set of key-value pairs.
jit?	When present, this directive/component is ignored by the AOT compiler. It remains in distributed code, and the JIT compiler attempts to compile it at run time, in the browser. To ensure the correct behavior, the app must import @angular/compiler.
standalone?	Angular directives marked as standalone do not need to be declared in an NgModule. Such directives don't depend on any "intermediate context" of an NgModule (ex. configured providers).
signals?	// TODO(signals): Remove internal and add public documentation
hostDirectives?	Standalone directives that should be applied to the host whenever the directive is matched. By default, none of the inputs or outputs of the host directives will be available on the host, unless they are specified in the inputs or outputs properties.

Description

Components are the most basic UI building block of an Angular app. An Angular app contains a tree of Angular components.

Angular components are a subset of directives, always associated with a template. Unlike other directives, only one component can be instantiated for a given element in a template.

A component must belong to an NgModule in order for it to be available to another component or application. To make it a member of an NgModule, list it in the declarations field of the NgModule metadata.

Note that, in addition to these options for configuring a directive, you can control a component's runtime behavior by implementing life-cycle hooks. For more information, see the Lifecycle Hooks guide.

Further information is available in the Usage Notes...

Options

changeDetection
The change-detection strategy to use for this component.
changeDetection?: ChangeDetectionStrategy
When a component is instantiated, Angular creates a change detector, which is responsible for propagating the component's bindings. The strategy is one of: ChangeDetectionStrategy#OnPush sets the strategy to CheckOnce (on demand). ChangeDetectionStrategy#Default sets the strategy to CheckAlways.

viewProviders
Defines the set of injectable objects that are visible to its view DOM children. See example.
viewProviders?: Provider[]

moduleId
The module ID of the module that contains the component. The component must be able to resolve relative URLs for templates and styles. SystemJS exposes the __moduleName variable within each module. In CommonJS, this can be set to module.id.
moduleId?: string

templateUrl
The relative path or absolute URL of a template file for an Angular component. If provided, do not supply an inline template using template.
templateUrl?: string

template
An inline template for an Angular component. If provided, do not supply a template file using templateUrl.
template?: string

styleUrls
One or more relative paths or absolute URLs for files containing CSS stylesheets to use in this component.
styleUrls?: string[]

styles
One or more inline CSS stylesheets to use in this component.
styles?: string[]

animations
One or more animation trigger() calls, containing state() and transition() definitions. See the Animations guide and animations API documentation.
animations?: any[]

encapsulation
An encapsulation policy for the component's styling. Possible values: ViewEncapsulation.Emulated: Apply modified component styles in order to emulate a native Shadow DOM CSS encapsulation behavior. ViewEncapsulation.None: Apply component styles globally without any sort of encapsulation. ViewEncapsulation.ShadowDom: Use the browser's native Shadow DOM API to encapsulate styles.
encapsulation?: ViewEncapsulation
If not supplied, the value is taken from the CompilerOptions which defaults to ViewEncapsulation.Emulated. If the policy is ViewEncapsulation.Emulated and the component has no Component#styles nor Component#styleUrls, the policy is automatically switched to ViewEncapsulation.None.

interpolation
Overrides the default interpolation start and end delimiters ({{ and }}).
interpolation?: [ string, string ]

preserveWhitespaces
True to preserve or false to remove potentially superfluous whitespace characters from the compiled template. Whitespace characters are those matching the \s character class in JavaScript regular expressions. Default is false, unless overridden in compiler options.
preserveWhitespaces?: boolean

standalone
Angular components marked as standalone do not need to be declared in an NgModule. Such components directly manage their own template dependencies (components, directives, and pipes used in a template) via the imports property.
standalone?: boolean
More information about standalone components, directives, and pipes can be found in this guide.

signals
// TODO(signals): Remove internal and add public documentation.
signals?: boolean

imports
The imports property specifies the standalone component's template dependencies — those directives, components, and pipes that can be used within its template. Standalone components can import other standalone components, directives, and pipes as well as existing NgModules.
imports?: (Type<any> | ReadonlyArray<any>)[]
This property is only available for standalone components - specifying it for components declared in an NgModule generates a compilation error. More information about standalone components, directives, and pipes can be found in this guide.

schemas
The set of schemas that declare elements to be allowed in a standalone component. Elements and properties that are neither Angular components nor directives must be declared in a schema.
schemas?: SchemaMetadata[]
This property is only available for standalone components - specifying it for components declared in an NgModule generates a compilation error. More information about standalone components, directives, and pipes can be found in this guide.

Usage notes

Setting component inputs

The following example creates a component with two data-bound properties, specified by the inputs value.

@Component({
  selector: 'app-bank-account',
  inputs: ['bankName', 'id: account-id'],
  template: `
    Bank Name: {{ bankName }}
    Account Id: {{ id }}
  `
})
export class BankAccountComponent {
  bankName: string|null = null;
  id: string|null = null;

  // this property is not bound, and won't be automatically updated by Angular
  normalizedBankName: string|null = null;
}

@Component({
  selector: 'app-my-input',
  template: `
    <app-bank-account
      bankName="RBC"
      account-id="4747">
    </app-bank-account>
  `
})
export class MyInputComponent {
}

Setting component outputs

The following example shows two event emitters that emit on an interval. One emits an output every second, while the other emits every five seconds.

@Directive({selector: 'app-interval-dir', outputs: ['everySecond', 'fiveSecs: everyFiveSeconds']})
export class IntervalDirComponent {
  everySecond = new EventEmitter<string>();
  fiveSecs = new EventEmitter<string>();

  constructor() {
    setInterval(() => this.everySecond.emit('event'), 1000);
    setInterval(() => this.fiveSecs.emit('event'), 5000);
  }
}

@Component({
  selector: 'app-my-output',
  template: `
    <app-interval-dir
      (everySecond)="onEverySecond()"
      (everyFiveSeconds)="onEveryFiveSeconds()">
    </app-interval-dir>
  `
})
export class MyOutputComponent {
  onEverySecond() {
    console.log('second');
  }
  onEveryFiveSeconds() {
    console.log('five seconds');
  }
}

Injecting a class with a view provider

The following simple example injects a class into a component using the view provider specified in component metadata:

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>`
})
class HelloWorld {
}

Preserving whitespace

Removing whitespace can greatly reduce AOT-generated code size and speed up view creation. As of Angular 6, the default for preserveWhitespaces is false (whitespace is removed). To change the default setting for all components in your application, set the preserveWhitespaces option of the AOT compiler.

By default, the AOT compiler removes whitespace characters as follows:

• Trims all whitespaces at the beginning and the end of a template.
• Removes whitespace-only text nodes. For example,

<button>Action 1</button>  <button>Action 2</button>

becomes:

<button>Action 1</button><button>Action 2</button>

• Replaces a series of whitespace characters in text nodes with a single space. For example, <span>\n some text\n</span> becomes <span> some text </span>.
• Does NOT alter text nodes inside HTML tags such as <pre> or <textarea>, where whitespace characters are significant.

Note that these transformations can influence DOM nodes layout, although impact should be minimal.

You can override the default behavior to preserve whitespace characters in certain fragments of a template. For example, you can exclude an entire DOM sub-tree by using the ngPreserveWhitespaces attribute:

<div ngPreserveWhitespaces>
    whitespaces are preserved here
    <span>    and here </span>
</div>

You can force a single space to be preserved in a text node by using &ngsp;, which is replaced with a space character by Angular's template compiler:

<a>Spaces</a>&ngsp;<a>between</a>&ngsp;<a>links.</a>
<!-- compiled to be equivalent to:
 <a>Spaces</a> <a>between</a> <a>links.</a>  -->

Note that sequences of &ngsp; are still collapsed to just one space character when the preserveWhitespaces option is set to false.

<a>before</a>&ngsp;&ngsp;&ngsp;<a>after</a>
<!-- compiled to be equivalent to:
 <a>before</a> <a>after</a> -->

To preserve sequences of whitespace characters, use the ngPreserveWhitespaces attribute.