From e6304cbbf3c78bf54c7d96fbcd943f72443c52ed Mon Sep 17 00:00:00 2001
From: Nolan Lawson <nolan@nolanlawson.com>
Date: Sat, 10 Feb 2018 11:30:13 -0800
Subject: [PATCH] use event delegation for better perf

---
 routes/_components/status/Status.html | 20 +++++++++--
 routes/_utils/delegate.js             | 50 +++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 2 deletions(-)
 create mode 100644 routes/_utils/delegate.js

diff --git a/routes/_components/status/Status.html b/routes/_components/status/Status.html
index 37ac102a..5c3262c3 100644
--- a/routes/_components/status/Status.html
+++ b/routes/_components/status/Status.html
@@ -1,6 +1,9 @@
 <article class="status-article {{getClasses(originalStatus, timelineType, isStatusInOwnThread)}}"
-         tabindex="0" on:click="onClickOrKeydown(event)" on:keydown="onClickOrKeydown(event)"
-         aria-posinset="{{index}}" aria-setsize="{{length}}"
+         tabindex="0"
+         delegate-click-key="{{delegateKey}}"
+         delegate-keydown-key="{{delegateKey}}"
+         aria-posinset="{{index}}"
+         aria-setsize="{{length}}"
          aria-label="Status by {{originalStatus.account.display_name || originalStatus.account.username}}"
          on:recalculateHeight>
   {{#if (notification && (notification.type === 'reblog' || notification.type === 'favourite')) || status.reblog}}
@@ -87,8 +90,20 @@
   import { store } from '../../_store/store'
   import identity from 'lodash/identity'
   import { goto } from 'sapper/runtime.js'
+  import { registerDelegate, unregisterDelegate } from '../../_utils/delegate'
 
   export default {
+    oncreate() {
+      let delegateKey = this.get('delegateKey')
+      let onClickOrKeydown = this.onClickOrKeydown.bind(this)
+      registerDelegate('click', delegateKey, onClickOrKeydown)
+      registerDelegate('keydown', delegateKey, onClickOrKeydown)
+    },
+    ondestroy() {
+      let delegateKey = this.get('delegateKey')
+      unregisterDelegate('click', delegateKey)
+      unregisterDelegate('keydown', delegateKey)
+    },
     components: {
       StatusSidebar,
       StatusHeader,
@@ -132,6 +147,7 @@
     computed: {
       originalStatus: (status) => status.reblog ? status.reblog : status,
       statusId: (originalStatus) => originalStatus.id,
+      delegateKey: (statusId, timelineType, timelineValue) => `status-${timelineType}-${timelineValue}-${statusId}`,
       contextualStatusId: ($currentInstance, timelineType, timelineValue, status, notification) => {
         return `${$currentInstance}/${timelineType}/${timelineValue}/${notification ? notification.id : ''}/${status.id}`
       },
diff --git a/routes/_utils/delegate.js b/routes/_utils/delegate.js
new file mode 100644
index 00000000..d12d2331
--- /dev/null
+++ b/routes/_utils/delegate.js
@@ -0,0 +1,50 @@
+// Delegate certain events to the global document for perf purposes.
+
+import { mark, stop } from './marks'
+
+const callbacks = {}
+
+if (process.browser && process.env.NODE_ENV !== 'production') {
+  window.delegateCallbacks = callbacks
+}
+
+function onEvent(e) {
+  let { type, keyCode, target } = e
+  if (!(type === 'click' || (type === 'keydown' && keyCode === 13))) {
+    // we're not interested in any non-click or non-Enter events
+    return
+  }
+  mark('delegate onEvent')
+  let attr = `delegate-${type}-key`
+  let key
+  let element = target
+  while (element) {
+    if ((key = element.getAttribute(attr))) {
+      break
+    }
+    element = element.parentElement
+  }
+  if (key && callbacks[type] && callbacks[type][key]) {
+    callbacks[type][key](e)
+  }
+  stop('delegate onEvent')
+}
+
+export function registerDelegate(type, key, callback) {
+  mark('delegate registerDelegate')
+  callbacks[type] = callbacks[type] || {}
+  callbacks[type][key] = callback
+  stop('delegate registerDelegate')
+}
+
+export function unregisterDelegate(type, key) {
+  mark('delegate unregisterDelegate')
+  callbacks[type] = callbacks[type] || {}
+  delete callbacks[type][key]
+  stop('delegate unregisterDelegate')
+}
+
+if (process.browser) {
+  document.addEventListener('click', onEvent)
+  document.addEventListener('keydown', onEvent)
+}
\ No newline at end of file