Angular’s output interop helpers handle two opposite conversions: use outputFromObservable() to expose an RxJS Observable as a component or directive output, and outputToObservable() to turn an Angular output into an Observable for RxJS operators. If component code simply needs to emit an event imperatively, use output() and call .emit().
Choose the API by the direction of the event
| What you need | API | Result |
|---|---|---|
| Component or directive code decides when an event occurs | output<T>() |
An Angular OutputEmitterRef<T>, emitted with .emit(value). |
| An existing Observable should be available to a parent as an Angular output | outputFromObservable(source$) |
Angular forwards values from the Observable through the component or directive output. |
| An Angular output needs to be composed with RxJS operators | outputToObservable(outputRef) |
An RxJS Observable<T> representing output values. |
The two interop helpers are not interchangeable: outputFromObservable() goes from RxJS to Angular’s output system; outputToObservable() goes from an Angular output to RxJS. See Angular’s output interop guide for the supported patterns.
Declare an output for imperative emissions
For an event decided by component or directive code, declare output() as a class property initializer. Angular recognizes it as an output declaration, and the returned OutputEmitterRef provides .emit().
import { Component, output } from '@angular/core';
@Component({
selector: 'app-counter',
template: '<button (click)="increment()">Add</button>'
})
export class CounterComponent {
countChanged = output<number>();
private count = 0;
increment() {
this.countChanged.emit(++this.count);
}
}A parent can listen using Angular template event binding, for example <app-counter (countChanged)="onCountChanged($event)" />, or subscribe programmatically through the output reference. Angular’s API reference marks output() stable since Angular v19.0; check the API documentation for the version installed in your project before adopting it.
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Expose an Observable as a component output
Use outputFromObservable(source$) when an Observable already represents the values the parent should receive. Declare the helper in a component or directive property initializer:
import { Component } from '@angular/core';
import { outputFromObservable } from '@angular/core/rxjs-interop';
@Component({
selector: 'app-pointer',
template: ''
})
export class PointerComponent {
pointerMove = outputFromObservable(pointerMoves$);
}Here, pointerMoves$ stands for an Observable available in the class; supply the appropriate stream and imports for your application. Angular forwards its values to consumers of pointerMove, and stops forwarding when the component or directive is destroyed.
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Handle errors and completion in the stream
Angular does not handle errors from the source Observable for you. Decide how the stream should manage errors—for example, catch or otherwise handle them before passing it to outputFromObservable(). Once the source completes, it stops producing further output values. These behaviors are documented in Angular’s output interop guide.
Convert an Angular output to an Observable
Use outputToObservable() when you need RxJS operators or composition on values emitted by an Angular output. It returns an Observable:
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import { output, outputToObservable } from '@angular/core';
valueChange = output<string>();
valueChanges$ = outputToObservable(this.valueChange);Use the Observable as the source for the RxJS pipeline your code needs. If all you need is to run a callback for each value, subscribing directly to the output with OutputRef.subscribe() is simpler; Angular documents this option in the component outputs guide.
Understand naming, inheritance, and template behavior
- Angular custom outputs do not bubble through the DOM. A listener must be attached to the component or directive that declares the output.
- Output names are case-sensitive.
- An alias changes the name used in the template, not the TypeScript property name.
- Outputs declared by a base component are inherited by child classes.
- Angular recommends camelCase names without an
onprefix and advises against names that collide with native DOM events.
These conventions apply to component outputs generally, including outputs declared with the newer function API. Consult Angular’s outputs guide for template binding details.
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Keep or migrate legacy EventEmitter outputs
@Output() with EventEmitter<T> remains supported. EventEmitter extends RxJS Subject and includes .emit(). Angular recommends output() for new projects, but existing declarations do not need to be converted just to keep working. The outputs guide describes both approaches.
Run the migration schematic carefully
Angular CLI provides a schematic for eligible declarations:
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Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
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ng generate @angular/core:output-migrationIt can update eligible @Output() members and imports, change certain .next() calls to .emit(), and remove .complete() calls. It does not cover every usage pattern. Angular’s migration documentation says that output usages with .pipe() are not converted outside recognized test files. For tests, the schematic may rewrite piped usage to outputToObservable(...); its documented test-file recognition looks for imports containing jasmine or catalyst.
- Run the command from the Angular project you intend to migrate.
- If needed, use
--pathto limit the files changed. This does not guarantee that references outside the selected files are updated. - Use
--analysis-dironly when you understand its effect: references beyond that directory may be skipped and can leave the build broken. - Review the diff for usages the schematic did not convert, especially RxJS
.pipe()calls and references outside a narrowed analysis directory. - Run the project’s tests and build, then address any remaining references manually.
The schematic automates common changes rather than guaranteeing a complete migration; its options and limitations are detailed in the official migration guide.
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