Angular Event Plugins

@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
   
   @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

   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>
   </div>

3. You can also re-enter NgZone and trigger change detection, using @shouldCall decorator that takes a predicate function as argument:

<div (scroll.silent)="onScroll($event.currentTarget)">
    Scrolling this DIV will only trigger change detection and onScroll callback if it is
    scrolled to bottom
</div>

import {HostListener} from '@angular/core';
import {shouldCall} from '@tinkoff/ng-event-plugins';

export function scrollFilter(element: HTMLElement): boolean {
    return element.scrollTop === element.scrollHeight - element.clientHeight;
}

// ...

@shouldCall(scrollFilter)
@HostListener('init.onScroll', ['$event'])
onScroll(_element: HTMLElement) {
    this.someService.requestMoreData();
}

IMPORTANT: You must couple @shouldCall with @HostListener for init event as shown above until markDirty becomes public API in Angular and @tinkoff/ng-event-plugins v.3 is released

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 [link coming soon].

To use it you need to couple @HostListener and @HostBinding on the same Observable property with following syntax:

@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:

@HostBinding('$.aria-label.attr')
@HostListener('$.aria-label.attr')
readonly label$ = asCallable(this.translations.get$('label'));

Demo

You can try this interactive demo

You can also read this detailed article explaining how this library works

Open-source

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.