ng-lazy-load

ng-lazy-load library provides lazyLoad directive and LazyLoadService to lazy load your resource file when it is near to be shown on screen. This library is an extension of @trademe/ng-defer-load to allow more control on its behaviour and make it useful in ngFor loop. The library will output debug logs to console in the development mode to show what's happening inside the library:

...
lazyLoad never
lazyLoad register
loading [0] (Intersecting)
loading [1] (NearIntersecting 0)
loading [2] (NearIntersecting 0)
loading [5] (Intersecting)
...

Usage

Simplest usage would be:

<div (lazyLoad)="toLoad=true">
  <img [src]="toLoad ? url : ''">
</div>

A typical usage for ngFor loop would be:

<my-element #myElement
    *ngFor="let item of items$ | async; let i = index"
    (lazyLoad)="myElement.doLoad($event)" [url]="item.url" [index]="i" >
</my-element>

// in my-element component
import { IntersectionState } from 'ng-lazy-load';

doLoad(state: IntersectionState) {
  this.toLoad = true;
}

By having additional [url] and [index] inputs, the directive can choose to register the api only for elements that has a resource to load and provide some flexibility in its behaviour to cope with various needs.

LazyLoadService.loadAheadCount

Default value of LazyLoadService.loadAheadCount property is 2 which means that if [n]th element is intersecting, [n+1]th and [n+2]th elements will also be loaded as well. You can override this by setting to other value:

// in parent component
import { LazyLoadService } from 'ng-lazy-load';

constructor(private lazyLoadService: LazyLoadService) { }

ngOnInit() {
  this.lazyLoadService.loadAheadCount = 5; // load 5 elements ahead beyond the intersecting one

LazyLoadService.registerAfter()

By default, lazyLoad directive will register the IntersectionObserver api on its host element's init. But you may want to delay its registration:

// in parent component
ngOnInit() {
  this.lazyLoadService.registerAfter(1500); // let directives register after 1500 msec 

LazyLoadService.registerLater() and LazyLoadService.registerAll()

Or let directives register later when asked by the parent component:

// in parent component
ngOnInit() {
  this.lazyLoadService.registerLater(); // let directives not register on init
}
// somewhere in parent component
this.lazyLoadService.registerAll(); // let directives register now

A Stackblitz demo is available to show the usage.

Installation

// to install
npm install ng-lazy-load

// in app.module.ts
import { LazyLoadModule } from 'ng-lazy-load';
@NgModule({
  imports: [
    LazyLoadModule,

// in template
<div (lazyLoad)="toLoad=true">
  <img [src]="toLoad ? url : ''">