start on virtual list

package-lock.json

@@ -6829,9 +6829,7 @@
       "integrity": "sha1-U10EXOa2Nj+kARcIRimZXp3zJMc="
     },
     "svelte": {
-      "version": "1.51.0",
-      "resolved": "https://registry.npmjs.org/svelte/-/svelte-1.51.0.tgz",
-      "integrity": "sha512-lqa9eAZ4ZQLMWsoyynAogUtib7HhHnrJJaS93uRgZU5cfXquBVR+FkKVK41LdlwffmOfOjbUin6pT8e/LZUwjA=="
+      "version": "github:nolanlawson/svelte#c5cd9fc76e069faa364e5c2c6343ddaf2adc4dcf"
     },
     "svelte-extras": {
       "version": "1.6.0",

package.json

@@ -31,10 +31,10 @@
     "npm-run-all": "^4.1.2",
     "performance-now": "^2.1.0",
     "pify": "^3.0.0",
-    "sapper": "^0.3.1",
+    "sapper": "^0.3.2",
     "serve-static": "^1.13.1",
     "style-loader": "^0.19.1",
-    "svelte": "^1.50.0",
+    "svelte": "github:nolanlawson/svelte#master-8057884",
     "svelte-extras": "^1.6.0",
     "svelte-loader": "^2.3.3",
     "svelte-transitions": "^1.1.1",

routes/_components/StatusListItem.html

@@ -0,0 +1,17 @@
+<div class="list-item">
+  <Status status="{{virtualProps}}" />
+</div>
+<style>
+  .list-item {
+    border-bottom: 1px solid var(--main-border);
+  }
+</style>
+<script>
+  import Status from './Status.html'
+
+  export default {
+    components: {
+      Status
+    }
+  }
+</script>

routes/_components/Timeline.html

@@ -1,33 +1,27 @@
-<ul>
-  {{#each statuses as status}}
-  <li>
-    <Status :status />
-  </li>
-  {{/each}}
-</ul>
+<div class="timeline">
+  <VirtualList component="{{StatusListItem}}" items="{{statuses}}" />
+</div>
 <style>
-  ul {
-    list-style: none;
+  .timeline {
     padding-right: 10px;
   }
-  li {
-    border-bottom: 1px solid var(--main-border);
-  }
 </style>
 <script>
   import { store } from '../_utils/store'
   import { getHomeTimeline } from '../_utils/mastodon/oauth'
   import fixture from '../_utils/fixture.json'
-  import Status from './Status.html'
+  import StatusListItem from './StatusListItem.html'
+  import VirtualList from './VirtualList.html'
 
   export default {
     data: () => ({
       target: 'home',
-      statuses: fixture
+      statuses: fixture,
+      StatusListItem: StatusListItem
     }),
     store: () => store,
     components: {
-      Status
+      VirtualList
     }
   }
 </script>

routes/_components/VirtualList.html

@@ -0,0 +1,70 @@
+<div class="virtual-list" ref:node style="height: {{height}}px;">
+  {{#each visibleItems as visibleItem, index}}
+    <VirtualListItem :component
+                     :intersectionObserver
+                     virtualOffset="{{visibleItem.offset}}"
+                     virtualProps="{{visibleItem.props}}"
+                     virtualIndex="{{index}}" />
+  {{/each}}
+</div>
+<style>
+  .virtual-list {
+    position: relative;
+  }
+</style>
+<script>
+  import VirtualListItem from './VirtualListItem'
+
+  function sum(arr) {
+    return arr.reduce((a, b) => a + b, 0)
+  }
+
+  export default {
+    oncreate() {
+      let intersectionObserver = new IntersectionObserver((entries) => {
+        let totalHeight = sum(entries.map(entry => entry.boundingClientRect.height))
+        let offset = 0
+        let offsets = []
+        entries.forEach(entry => {
+          offsets.push(offset)
+          offset += entry.boundingClientRect.height
+        })
+        this.set({
+          height: totalHeight,
+          offsets: offsets
+        })
+        console.log('entries', entries.map(entry => entry.target.getAttribute('data-virtual-index')))
+      }, {
+        root: this.refs.node
+      })
+      this.set({
+        intersectionObserver: intersectionObserver
+      })
+    },
+    ondestroy() {
+      let intersectionObserver = this.get('intersectionObserver')
+      if (intersectionObserver) {
+        intersectionObserver.disconnect()
+      }
+    },
+    computed: {
+      visibleItems: (items, offsets) => {
+        return items.map((item, idx) => ({
+          props: item,
+          offset: offsets[idx]
+        }))
+      }
+    },
+    data: () => ({
+      scrollHeight: 0,
+      component: null,
+      intersectionObserver: null,
+      items: [],
+      offsets: [],
+      height: 400
+    }),
+    components: {
+      VirtualListItem
+    }
+  }
+</script>

routes/_components/VirtualListItem.html

@@ -0,0 +1,29 @@
+<div class="virtual-list-item"
+     ref:node
+     style="transform: translate3d(0, {{virtualOffset}}px, 0);"
+     data-virtual-index="{{virtualIndex}}">
+  <:Component {component} :virtualProps :virtualIndex :intersectionObserver />
+</div>
+<style>
+  .virtual-list-item {
+    position: absolute;
+    top: 0;
+    will-change: transform;
+  }
+</style>
+<script>
+  export default {
+    oncreate() {
+      this.observe('intersectionObserver', (intersectionObserver) => {
+        if (intersectionObserver) {
+          intersectionObserver.observe(this.refs.node)
+        }
+      })
+    },
+    methods: {
+      showRefs () {
+        console.log(this.refs)
+      }
+    }
+  }
+</script>