Angular Event Filters

@tinkoff/ng-event-filters 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 new providers to your app module:

   import {NgModule} from '@angular/core';
   import {PLUGINS} from '@tinkoff/ng-event-filters'; // <-- THIS
   
   @NgModule({
       bootstrap: [
           /*...*/
       ],
       imports: [
           /*...*/
       ],
       declarations: [
           /*...*/
       ],
       providers: [...PLUGINS], // <-- GOES HERE
   })
   export class AppModule {}

2. Use new modifiers for events in templates and in @HostListener:

   • .stop to call stopPropagation() on event
   • .prevent to call preventDefault() on event
   • .silent to call event handler outside Angular's NgZone

   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>

3. You can also re-enter NgZone and trigger change detection, using @filter decorator:

<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 {filter} from '@tinkoff/ng-event-filters';

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

// ...

@filter(scrollFilter)
onScroll(_element: HTMLElement) {
    this.someService.requestMoreData();
}

All examples above work the same when used with @HostListener.

Important notes

• Filter function will be called with the same arguments as the decorated method. Decorated method will be called and change detection triggered if filter function returns true.

• Filter function 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.

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.