perf: use requestPostAnimationFrame to reduce layout thrashing (#1376)

src/routes/_components/compose/ComposeInput.html

@@ -69,6 +69,7 @@
   import { observe } from 'svelte-extras'
   import { get } from '../../_utils/lodash-lite'
   import { on } from '../../_utils/eventBus'
+  import { requestPostAnimationFrame } from '../../_utils/requestPostAnimationFrame'
 
   export default {
     oncreate () {
@@ -117,7 +118,7 @@
       },
       setupAutosize () {
         const textarea = this.refs.textarea
-        requestAnimationFrame(() => {
+        requestPostAnimationFrame(() => {
           mark('autosize()')
           autosize(textarea)
           stop('autosize()')

src/routes/_components/virtualList/VirtualListItem.html

@@ -28,12 +28,13 @@
   import { virtualListStore } from './virtualListStore'
   import { registerResizeListener, unregisterResizeListener } from '../../_utils/resize'
   import { mark, stop } from '../../_utils/marks'
+  import { requestPostAnimationFrame } from '../../_utils/requestPostAnimationFrame'
 
   export default {
     oncreate () {
       const { key } = this.get()
       const node = this.refs.node
-      requestAnimationFrame(() => {
+      requestPostAnimationFrame(() => {
         if (!node || !key) {
           return
         }

src/routes/_utils/RealmStore.js

@@ -4,6 +4,7 @@
 import { Store } from 'svelte/store.js'
 import QuickLRU from 'quick-lru'
 import { mark, stop } from './marks'
+import { requestPostAnimationFrame } from './requestPostAnimationFrame'
 
 export class RealmStore extends Store {
   constructor (init, maxSize) {
@@ -47,7 +48,7 @@ export class RealmStore extends Store {
     }
     batch[subKey] = value
 
-    requestAnimationFrame(() => {
+    requestPostAnimationFrame(() => {
       const batch = this._batches[currentRealm] && this._batches[currentRealm][key]
       if (!batch) {
         return

src/routes/_utils/requestPostAnimationFrame.js

@@ -1,9 +1,33 @@
 // modeled after https://github.com/andrewiggins/afterframe
 // see also https://github.com/WICG/requestPostAnimationFrame
-export const requestPostAnimationFrame = cb => {
-  requestAnimationFrame(() => {
-    const channel = new MessageChannel()
-    channel.port1.onmessage = cb
-    channel.port2.postMessage(undefined)
-  })
+const channel = process.browser && new MessageChannel()
+const callbacks = []
+
+if (process.browser) {
+  channel.port1.onmessage = onMessage
+}
+
+function runCallback (callback) {
+  try {
+    callback()
+  } catch (e) {
+    console.error(e)
+  }
+}
+
+function onMessage () {
+  for (const callback of callbacks) {
+    runCallback(callback)
+  }
+  callbacks.length = 0
+}
+
+function postMessage () {
+  channel.port2.postMessage(undefined)
+}
+
+export const requestPostAnimationFrame = callback => {
+  if (callbacks.push(callback) === 1) {
+    requestAnimationFrame(postMessage)
+  }
 }