Introduce the group activity section

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/components/Utils/Observer.vue

@@ -0,0 +1,28 @@
+<template>
+  <div class="observer" />
+</template>
+
+<script lang="ts">
+import "intersection-observer";
+import { Component, Prop, Vue } from "vue-property-decorator";
+
+@Component
+export default class Observer extends Vue {
+  @Prop({ required: false, default: () => ({}) }) options!: Record<string, any>;
+
+  observer!: IntersectionObserver;
+  mounted(): void {
+    this.observer = new IntersectionObserver(([entry]) => {
+      if (entry && entry.isIntersecting) {
+        this.$emit("intersect");
+      }
+    }, this.options);
+
+    this.observer.observe(this.$el);
+  }
+
+  destroyed(): void {
+    this.observer.disconnect();
+  }
+}
+</script>