Creating custom events with outputs in Angular allows you to pass data and notify parent components about changes or interactions within child components. Custom events are often used within Angular components to facilitate this communication. This guide will walk you through the process of using Angular custom events with outputs, emitting events, and customizing event names for better maintainability and clarity in your Angular applications.

Defining Angular Custom Events with Outputs

Angular custom events with outputs can be defined by assigning a property to a new EventEmitter instance and adding the @Output decorator:

@Component({...})
export class ExpandablePanel {
  @Output() panelClosed = new EventEmitter<void>();
}
 

In the template, you can listen for this event and handle it with a method:

<expandable-panel (panelClosed)="savePanelState()"></expandable-panel>

 

This is an example of event binding, which connects the custom event to a method in the template.

To emit an event, call the emit method on the EventEmitter instance:

this.panelClosed.emit();
 

Emitting Event Data

Angular custom events with outputs can carry data by passing a value to the emit method. This value can be a primitive or a custom object:

// Emitting a primitive value
this.valueChanged.emit(7);


// Emitting a custom event object
this.thumbDropped.emit({ pointerX: 123, pointerY: 456 });
 

Event emitters are used to send data from child components to parent components, enabling effective communication and state management.

In the template, the event data is accessible via the $event variable:

<custom-slider (valueChanged)="logValue($event)"></custom-slider>

 

Customizing Output Names

The @Output decorator accepts a parameter to specify a different event name in the template for Angular custom events with outputs:

@Component({...})
export class CustomSlider {
  @Output('valueChanged') changed = new EventEmitter<number>();
}
 

You can then use the specified name in the template:

<custom-slider (valueChanged)="saveVolume()"></custom-slider>

Specifying Outputs in the @Component Decorator

 

You can list outputs in the decorator, which is useful when a component inherits properties from a base class:

@Component({
  ...,
  outputs: ['valueChanged'],
})
export class CustomSlider extends BaseSlider {}
 

Specifying outputs is particularly useful when creating a custom angular component that needs to communicate with other components.

You can also alias inherited outputs for Angular custom events with outputs:

@Component({
  ...,
  outputs: ['valueChanged: volumeChanged'],
})
export class CustomSlider extends BaseSlider {}
 

Choosing Event Names

When choosing names for Angular custom events with outputs, avoid collisions with native DOM events. Use camelCase and avoid prefixes like "on":

  • Good: valueChanged
  • Bad: onValueChanged, click

FAQs about Angular Custom Events with Outputs

What are Angular outputs?

Outputs are custom events defined in a component using the @Output decorator and EventEmitter.

How do you define an output in Angular?

@Output decorator and assign a property to a new EventEmitter instance.

Can custom events carry data?

Yes, you can pass data to the emit method of the EventEmitter.

How do you customize output names?

Pass the desired event name as a parameter to the @Output.

Can outputs be inherited?

Yes, outputs can be inherited from a base class and specified in the @Component decorator.

What is the $event variable?

$event is a template variable that holds the event data emitted by a custom event.

Why avoid prefixes for output names?

Prefixes like “on” can be confusing and are not necessary since a component’s outputs are unique.

Can you alias output names?

Yes, aliasing is useful for renaming properties or avoiding name collisions.

Are output names case-sensitive?

Yes, output names are case-sensitive.

Do Angular custom events bubble up the DOM?

No, Angular custom events do not bubble up the DOM.

How does the constructor create an instance for event handling?

The constructor creates an instance of a class capable of delivering events in both synchronous and asynchronous modes. This class is final and should not be extended. For more details, consult the public API notes.

How do you create custom events in Angular?

To create custom events in Angular, define output properties using the @Output decorator and EventEmitter. This process facilitates communication between child and parent components.

How do you implement your own custom events in Angular?

You can implement your own custom events in Angular by using the @Output() decorator to define custom events that can be emitted from child components. For example:

@Output() customEvent = new EventEmitter<string>();

This allows the child component to emit events that the parent component can catch.

How do parent components handle events from child components?

Parent components handle events from child components by listening for the events emitted by the child components. The parent can then respond to these events and update its own state or perform specified actions based on the data sent from the child.

Ready to leverage custom events in your Angular applications? Visit the T&S Software homepage for more tutorials and resources to enhance your development skills.

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