# Angular Event Plugins
[](https://npmjs.com/package/@tinkoff/ng-event-plugins)
[](https://bundlephobia.com/result?p=@tinkoff/ng-event-plugins)
[](https://app.codecov.io/gh/taiga-family/ng-event-plugins/tree/main/projects)
[](https://t.me/taiga_ui)
**@tinkoff/ng-event-plugins** is a tiny (1KB gzip) library for optimizing change detection cycles for performance
sensitive events (such as _touchmove_, _scroll_, _drag_ etc.) and declarative _preventDefault()_ and
_stopPropagation()_.
## How to use
1. Add `EventPluginsModule` to your app module:
```typescript
import {NgModule} from '@angular/core';
import {BrowserModule} from '@angular/platform-browser';
import {EventPluginsModule} from '@tinkoff/ng-event-plugins'; // <-- THIS
@NgModule({
bootstrap: [
/*...*/
],
imports: [
/*...*/
BrowserModule,
EventPluginsModule, // <-- GOES HERE
],
declarations: [
/*...*/
],
})
export class AppModule {}
```
> `BrowserModule` or `BrowserAnimationsModule` must go first. You will see a warning if you mess the order.
2. Use new modifiers for events in templates and in `@HostListener`:
- `.stop` to call stopPropagation() on event
- `.prevent` to call preventDefault() on event
- `.self` to skip bubbled events
- `.silent` to call event handler outside Angular's `NgZone`
- `.capture` to listen to events in
[capture phase](https://developer.mozilla.org/en-US/docs/Web/API/Event/eventPhase)
- `.passive` to add
[passive event listener](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#improving_scrolling_performance_with_passive_listeners)
- `.once` to remove event listener after first callback
For example:
```html
Clicking on this DIV will not move focus
```
```html
Clicks on this DIV will not bubble up
```
```html
Callbacks to mousemove will not trigger change detection
```
```html
Clicks will be stopped before reaching this DIV
```
3. You can also re-enter `NgZone` and trigger change detection, using `@shouldCall` decorator that takes a predicate
function as argument:
```html
Scrolling this DIV will only trigger change detection and onScroll callback if it is scrolled to bottom
```
```typescript
import {shouldCall} from '@tinkoff/ng-event-plugins';
export function scrollFilter({
scrollTop, scrollHeight, clientHeight
}: HTMLElement): boolean {
return scrollTop === scrollHeight - clientHeight;
}
// ...
@shouldCall(scrollFilter)
onScroll(_element: HTMLElement): void {
this.someService.requestMoreData();
}
```
4. Angular global events only support `body`, `window` and `document`. You can listen to events on any global object
with these plugins by replacing `:` with `>` symbol, for example:
```ts
@HostListener('visualViewport>resize', ['$event.target'])
onPinchZoom({ scale }: VisualViewport) {
console.log(scale)
}
```
> All examples above work the same when used with `@HostListener` and `CustomEvent`
### Important notes
- Predicate is called with the same arguments as the decorated method and in the context of class instance (has access
to `this`)
- Decorated method will be called and change detection triggered if predicate returns `true`.
- Predicates must be exported named function for AOT, arrow functions will trigger build error.
- `.silent` modifier will not work with built-in keyboard pseudo-events, such as `keydown.enter` or `keydown.arrowDown`
since Angular re-enters `NgZone` inside internal handlers.
## Observable host bindings
In this library there's also a plugin that enables observable host bindings. Sounds weird to do host binding with event
plugin, but the code is actually pretty simple. You can read more about it in
[this article](https://indepth.dev/posts/1429/making-hostbinding-work-with-observables).
To use it you need to couple `@HostListener` and `@HostBinding` on the same `Observable` property with following syntax:
```ts
@HostBinding('$.disabled')
@HostListener('$.disabled')
readonly disabled$ = asCallable(this.service.loading$)
```
This supports all the native Angular syntax, such as `class.class-name` or `style.width.px`.
**IMPORTANT NOTES:**
- Until [this issue](https://github.com/angular/angular/issues/12045) is resolved you would have to use
`NO_ERRORS_SCHEMA` in your module in order to bind to arbitrary properties
- `asCallable` is a utility function from this library that simply adds `Function` to the type so Angular thinks it
could be a host listener
- To bind attributes you need to add `.attr` modifier in the end, not the beginning like in basic Angular binding. This
is due to Angular using regexp to match for `attr.` string in `@HostBinding` decorator:
```ts
@HostBinding('$.aria-label.attr')
@HostListener('$.aria-label.attr')
readonly label$ = asCallable(this.translations.get$('label'));
```
## Demo
You can try this
[interactive demo](https://codesandbox.io/s/github/taiga-family/ng-event-plugins/tree/main/projects/demo)
You can also read this [detailed article](https://indepth.dev/supercharge-event-management-in-your-angular-application/)
explaining how this library works
## Maintained
**@tinkoff/ng-event-plugins** is a part of [Taiga UI](https://github.com/taiga-family/taiga-ui) libraries family which
is backed and used by a large enterprise. This means you can rely on timely support and continuous development.
## License
🆓 Feel free to use our library in your commercial and private applications
All **@tinkoff/ng-event-plugins** packages are covered by [Apache 2.0](/LICENSE)
Read more about this license [here](https://choosealicense.com/licenses/apache-2.0/)