fix: avoid many scrollTo calls for n components

Thank you @vbelolapotkov for pointing out the flaws here:
https://github.com/Human-Connection/Human-Connection/pull/1756#discussion_r329361572

So here is my attempt to fix it:
* Install `vue-scrollto` which relies on `requestAnimationFrame`
  - apparently this is better on Safari and IE? 🤔
  - Mocking out entire modules is easier in jest:
    https://jestjs.io/docs/en/bypassing-module-mocks
* Require `checkAnchor` to be implemented on the component

webapp/components/Comment/Comment.vue

@@ -10,7 +10,7 @@
     </ds-card>
   </div>
   <div v-else :class="{ comment: true, 'disabled-content': comment.deleted || comment.disabled }">
-    <ds-card :id="`commentId-${comment.id}`">
+    <ds-card :id="anchor">
       <ds-space margin-bottom="small" margin-top="small">
         <hc-user :user="author" :date-time="comment.createdAt" />
         <!-- Content Menu (can open Modals) -->
@@ -111,6 +111,9 @@ export default {
       user: 'auth/user',
       isModerator: 'auth/isModerator',
     }),
+    anchor() {
+      return `commentId-${this.comment.id}`
+    },
     displaysComment() {
       return !this.unavailable || this.isModerator
     },
@@ -144,6 +147,9 @@ export default {
     },
   },
   methods: {
+    checkAnchor(anchor) {
+      return `#${this.anchor}` === anchor
+    },
     isAuthor(id) {
       return this.user.id === id
     },

webapp/components/CommentList/CommentList.vue

@@ -41,6 +41,9 @@ export default {
     post: { type: Object, default: () => {} },
   },
   methods: {
+    checkAnchor(anchor) {
+      return anchor === '#comments'
+    },
     updateCommentList(updatedComment) {
       this.post.comments = this.post.comments.map(comment => {
         return comment.id === updatedComment.id ? updatedComment : comment

webapp/mixins/scrollToAnchor.js

@@ -1,32 +1,20 @@
-export function scrollToAnchor(anchor) {
-  if (!anchor) return
-  if (!window || !document) {
-    return
-  }
-  const container = document.querySelector(anchor)
-  if (container) {
-    const { top } = container.getBoundingClientRect()
-    setTimeout(() => {
-      // we have to set a small timeout to ensure this part comes after nuxt
-      // scrollBehaviour: https://nuxtjs.org/api/configuration-router/#scrollbehavior
-      window.scroll({
-        top,
-        left: 0,
-        behavior: 'smooth',
-      })
-    }, 250)
-  }
-}
+import { scrollTo } from 'vue-scrollto'
 
 export default {
   watch: {
     $route(to, from) {
       const anchor = to && to.hash
-      scrollToAnchor(anchor)
+      if (!this.checkAnchor(anchor)) return
+      setTimeout(() => {
+        scrollTo(anchor, 1000)
+      }, 250)
     },
   },
   mounted() {
     const anchor = this.$route && this.$route.hash
-    scrollToAnchor(anchor)
+    if (!this.checkAnchor(anchor)) return
+    setTimeout(() => {
+      scrollTo(anchor, 1000)
+    }, 250)
   },
 }

webapp/mixins/scrollToAnchor.spec.js

@@ -0,0 +1,47 @@
+import { scrollTo } from 'vue-scrollto'
+import scrollToAnchor from './scrollToAnchor'
+jest.mock('vue-scrollto')
+
+let component
+
+describe('scrollToAnchor', () => {
+  beforeEach(() => {
+    jest.useFakeTimers()
+    scrollTo.mockClear()
+  })
+
+  describe('scrollToAnchor', () => {
+    const action = hash => {
+      let {
+        watch: { $route },
+      } = scrollToAnchor
+      $route.bind(component)({ hash })
+      jest.runAllTimers()
+    }
+
+    describe('given anchor `commentId-4711`', () => {
+      beforeEach(() => {
+        component = {
+          anchor: 'commentId-4711',
+          checkAnchor(anchor) {
+            return this.anchor === anchor
+          },
+        }
+      })
+
+      describe('$route.hash === anchor', () => {
+        it('calls window.scroll', () => {
+          action('commentId-4711')
+          expect(scrollTo).toHaveBeenCalled()
+        })
+      })
+
+      describe('$route.hash !== anchor', () => {
+        it('skips window.scroll', () => {
+          action('commentId-4712')
+          expect(scrollTo).not.toHaveBeenCalled()
+        })
+      })
+    })
+  })
+})

webapp/package.json

@@ -83,6 +83,7 @@
     "vue-count-to": "~1.0.13",
     "vue-infinite-scroll": "^2.0.2",
     "vue-izitoast": "^1.2.1",
+    "vue-scrollto": "^2.17.1",
     "vue-sweetalert-icons": "~4.2.0",
     "vuex-i18n": "~1.13.1",
     "xregexp": "^4.2.4",

webapp/yarn.lock

@@ -4235,6 +4235,11 @@ bcrypt-pbkdf@^1.0.0:
   dependencies:
     tweetnacl "^0.14.3"
 
+bezier-easing@2.1.0:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/bezier-easing/-/bezier-easing-2.1.0.tgz#c04dfe8b926d6ecaca1813d69ff179b7c2025d86"
+  integrity sha1-wE3+i5JtbsrKGBPWn/F5t8ICXYY=
+
 bfj@^6.1.1:
   version "6.1.1"
   resolved "https://registry.yarnpkg.com/bfj/-/bfj-6.1.1.tgz#05a3b7784fbd72cfa3c22e56002ef99336516c48"
@@ -15315,6 +15320,13 @@ vue-router@~3.0.7:
   resolved "https://registry.yarnpkg.com/vue-router/-/vue-router-3.0.7.tgz#b36ca107b4acb8ff5bc4ff824584059c23fcb87b"
   integrity sha512-utJ+QR3YlIC/6x6xq17UMXeAfxEvXA0VKD3PiSio7hBOZNusA1jXcbxZxVEfJunLp48oonjTepY8ORoIlRx/EQ==
 
+vue-scrollto@^2.17.1:
+  version "2.17.1"
+  resolved "https://registry.yarnpkg.com/vue-scrollto/-/vue-scrollto-2.17.1.tgz#cd62ee0b98cf7e2ba9fd94f029addcd093978a48"
+  integrity sha512-uxOJXg6cZL88B+hTXRHDJMR+gHGiaS70ZTNk55fE5Z2TdwyIx9K/IHoNeTrtBrM6u3FASAIymKjZaQLmDf8Ykg==
+  dependencies:
+    bezier-easing "2.1.0"
+
 vue-server-renderer@^2.6.10:
   version "2.6.10"
   resolved "https://registry.yarnpkg.com/vue-server-renderer/-/vue-server-renderer-2.6.10.tgz#cb2558842ead360ae2ec1f3719b75564a805b375"