3 files changed, 80 insertions, 0 deletions

diff --git a/client/src/app/shared/shared-main/angular/defer-loading.directive.ts b/client/src/app/shared/shared-main/angular/defer-loading.directive.ts
new file mode 100644
index 000000000..9a10e90e3
--- /dev/null
+++ b/client/src/app/shared/shared-main/angular/defer-loading.directive.ts
@@ -0,0 +1,76 @@
+import * as debug from 'debug'
+import {
+  AfterViewInit,
+  ChangeDetectorRef,
+  ContentChild,
+  Directive,
+  ElementRef,
+  EmbeddedViewRef,
+  EventEmitter,
+  OnDestroy,
+  Output,
+  TemplateRef,
+  ViewContainerRef
+} from '@angular/core'
+
+const logger = debug('peertube:main:DeferLoadingDirective')
+
+@Directive({
+  selector: '[myDeferLoading]'
+})
+export class DeferLoadingDirective implements AfterViewInit, OnDestroy {
+  @ContentChild(TemplateRef) template: TemplateRef<any>
+
+  @Output() loaded: EventEmitter<any> = new EventEmitter()
+
+  view: EmbeddedViewRef<any>
+
+  private observer: IntersectionObserver
+
+  constructor (
+    private el: ElementRef,
+    private viewContainer: ViewContainerRef,
+    private cd: ChangeDetectorRef
+  ) { }
+
+  ngAfterViewInit () {
+    if (this.hasIncompatibleBrowser()) {
+      return this.load()
+    }
+
+    this.observer = new IntersectionObserver(entries => {
+      const entry = entries[0]
+      if (!entry.isIntersecting || entry.target !== this.el.nativeElement) return
+
+      this.observer.unobserve(this.el.nativeElement)
+      this.load()
+    }, { threshold: 0.1 })
+
+    this.observer.observe(this.el.nativeElement)
+  }
+
+  load () {
+    if (this.isLoaded()) return
+
+    logger('Loading component')
+
+    this.viewContainer.clear()
+    this.view = this.viewContainer.createEmbeddedView(this.template, {}, 0)
+    this.loaded.emit()
+    this.cd.detectChanges()
+  }
+
+  isLoaded () {
+    return this.view != null
+  }
+
+  ngOnDestroy () {
+    this.view = null
+
+    if (this.observer) this.observer.disconnect()
+  }
+
+  private hasIncompatibleBrowser () {
+    return !('IntersectionObserver' in window)
+  }
+}
diff --git a/client/src/app/shared/shared-main/angular/index.ts b/client/src/app/shared/shared-main/angular/index.ts
index 069b7f654..4b87c2952 100644
--- a/client/src/app/shared/shared-main/angular/index.ts
+++ b/client/src/app/shared/shared-main/angular/index.ts
@@ -1,5 +1,6 @@
 export * from './autofocus.directive'
 export * from './bytes.pipe'
+export * from './defer-loading.directive'
 export * from './duration-formatter.pipe'
 export * from './from-now.pipe'
 export * from './infinite-scroller.directive'
diff --git a/client/src/app/shared/shared-main/shared-main.module.ts b/client/src/app/shared/shared-main/shared-main.module.ts
index 10fc364b3..d83af9a66 100644
--- a/client/src/app/shared/shared-main/shared-main.module.ts
+++ b/client/src/app/shared/shared-main/shared-main.module.ts
@@ -21,6 +21,7 @@ import { AccountService } from './account'
 import {
   AutofocusDirective,
   BytesPipe,
+  DeferLoadingDirective,
   DurationFormatterPipe,
   FromNowPipe,
   InfiniteScrollerDirective,
@@ -80,6 +81,7 @@ import { VideoChannelService } from './video-channel'
     BytesPipe,
     DurationFormatterPipe,
     AutofocusDirective,
+    DeferLoadingDirective,
 
     InfiniteScrollerDirective,
     PeerTubeTemplateDirective,
@@ -139,6 +141,7 @@ import { VideoChannelService } from './video-channel'
     NumberFormatterPipe,
     DurationFormatterPipe,
     AutofocusDirective,
+    DeferLoadingDirective,
 
     InfiniteScrollerDirective,
     PeerTubeTemplateDirective,