This is a library for optimizing performance sensitive events and declarative preventDefault and stopPropagation

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Angular Event Plugins
npm version npm bundle size Build Status Coverage Status angular-open-source-starter @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:
import {NgModule} from '@angular/core';
import {BrowserModule} from '@angular/platform-browser';
import {EventPluginsModule} from '@tinkoff/ng-event-plugins'; // <-- THIS
bootstrap: [
imports: [
EventPluginsModule, // <-- GOES HERE
declarations: [
export class AppModule {}
BrowserModule or BrowserAnimationsModule must go first. You will see a warning if you mess the order.
  1. 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:
<div (mousedown.prevent)="onMouseDown()">Clicking on this DIV will not move focus</div>
<div (click.stop)="onClick()">Clicks on this DIV will not bubble up</div>
<div (mousemove.silent)="onMouseMove()">Callbacks to mousemove will not trigger change detection</div>
<div (click.capture.stop)="onClick()">
<div (click)="never()">Clicks will be stopped before reaching this DIV</div>
  1. You can also re-enter NgZone and trigger change detection, using @shouldCall decorator that takes a predicate
function as argument:
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 {
} ```
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
. 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$) ``` This supports all the native Angular syntax, such as class.class-name or style.width.px. IMPORTANT NOTES:
  • Until this issue is resolved you would have to use
NO_ERRORS_SCHEMA in your module in order to bind to arbitrary properties
  • asCallable is a utility function from this library that simply adds Function to the type so Angular thinks it
could be a host listener
  • To bind attributes you need to add .attr modifier in the end, not the beginning like in basic Angular binding. This
is due to Angular using regexp to match for attr. string in @HostBinding decorator: ```ts @HostBinding('$.aria-label.attr') @HostListener('$.aria-label.attr') readonly label$ = asCallable(this.translations.get$('label')); ```


You can try this interactive demo You can also read this detailed article explaining how this library works


Do you also want to open-source something, but hate the collateral work? Check out this Angular Open-source Library Starter we’ve created for our projects. It got you covered on continuous integration, pre-commit checks, linting, versioning + changelog, code coverage and all that jazz.