frontend: improve channel switch latency by reducing reflows due to scroll-related getters

frontend/src/components/pages/main/Message.svelte

@@ -0,0 +1,28 @@
+<script>
+    export let message;
+</script>
+
+<style>
+    .message {
+        overflow-x: none;
+        word-break: break-all;
+    }
+
+    .message-content {
+        color: var(--foreground-color-2);
+    }
+
+    .pending {
+        color: var(--foreground-color-3);
+    }
+
+    .author {
+        font-weight: bold;
+        margin-right: var(--space-xxs);
+    }
+</style>
+
+<div class="message">
+    <span class="author">{ message.author_username }</span>
+    <span class="message-content" class:pending={ message._isPending }>{ message.content }</span>
+</div>

frontend/src/components/pages/main/Messages.svelte

@@ -1,18 +1,16 @@
 <script>
-    import { afterUpdate, beforeUpdate } from "svelte";
+    import { afterUpdate, beforeUpdate, onMount } from "svelte";
     import { messagesStoreProvider } from "../../../stores.js";
+    import Message from "./Message.svelte";
 
     export let channelId;
     let scrollTarget;
-    let shouldAutoscroll = false;
+    let scrollAnchor;
+    let shouldAutoscroll = true;
     let lastScrollHeight = null;
 
     $: messages = messagesStoreProvider.getStore(channelId);
 
-    beforeUpdate(() => {
-        shouldAutoscroll = scrollTarget && (scrollTarget.offsetHeight + scrollTarget.scrollTop) > (scrollTarget.scrollHeight - 20);
-    });
-
     afterUpdate(() => {
         // hacky way to preserve scroll position when messages are pushed back
         if (lastScrollHeight) {
@@ -20,8 +18,8 @@
             lastScrollHeight = null;
             return;
         }
-        if (shouldAutoscroll && scrollTarget) {
-            scrollTarget.scrollTo(0, scrollTarget.scrollHeight);
+        if (shouldAutoscroll && scrollAnchor) {
+            scrollAnchor.scrollIntoView(false);
         }
     });
 
@@ -29,7 +27,9 @@
         const { scrollTop, offsetHeight, scrollHeight } = e.target;
         if ((scrollTop + offsetHeight) >= scrollHeight) { // user scrolled to bottom
             messages.setIsCollectingOldMessages(true);
+            shouldAutoscroll = true;
         } else {
+            shouldAutoscroll = false;
             if (scrollTop === 0) {
                 // load older messages if the user scrolls to the top.
                 // save the current scroll height if the server returned any messages,
@@ -57,31 +57,11 @@
         overflow-x: hidden;
         background-color: var(--background-color-1);
     }
-
-    .message {
-        overflow-x: none;
-        word-break: break-all;
-    }
-
-    .message-content {
-        color: var(--foreground-color-2);
-    }
-
-    .pending {
-        color: var(--foreground-color-3);
-    }
-
-    .author {
-        font-weight: bold;
-        margin-right: var(--space-xxs);
-    }
 </style>
 
 <div class="messages-container" on:scroll={ onScroll } bind:this={ scrollTarget }>
     {#each $messages as message (message.id)}
-        <div class="message">
-            <span class="author">{ message.author_username }</span>
-            <span class="message-content" class:pending={ message._isPending }>{ message.content }</span>
-        </div>
+        <Message message={message} />
     {/each}
+    <div bind:this={ scrollAnchor } />
 </div>

frontend/src/gateway.js

@@ -1,3 +1,4 @@
+import logging from "./logging";
 import { getAuthToken, getItem } from "./storage";
 
 export const GatewayPayloadType = {
@@ -22,6 +23,8 @@ export const GatewayEventType = {
     Close: -4
 }
 
+const log = logging.logger("Gateway");
+
 export default {
     ws: null,
     authenticated: false,
@@ -33,8 +36,6 @@ export default {
     reconnectTimeout: null,
     handlers: new Map(),
     init() {
-        window.__WAFFLE_GATEWAY = this;
-
         const token = getAuthToken();
         if (!token) {
             return false;
@@ -46,7 +47,7 @@ export default {
             }
             this.open = true;
             this.dispatch(GatewayEventType.Open, null);
-            console.log("[gateway] open");
+            log("open");
         };
         this.ws.onmessage = (event) => {
             const payload = JSON.parse(event.data);
@@ -65,7 +66,7 @@ export default {
                         });
                     }, payload.d.pingInterval);
 
-                    console.log("[gateway] hello");
+                    log("hello");
                     break;
                 }
                 case GatewayPayloadType.Ready: {
@@ -74,7 +75,7 @@ export default {
 
                     this.reconnectDelay = 400;
 
-                    console.log("[gateway] ready");
+                    log("ready");
                     break;
                 }
             }
@@ -98,7 +99,7 @@ export default {
 
             this.dispatch(GatewayEventType.Close, null);
 
-            console.log("[gateway] close");
+            log("close");
         };
 
         return true;

frontend/src/logging.js

@@ -0,0 +1,21 @@
+export default {
+    sinks: new Map(),
+    logger(sink, enabled=false) {
+        this.sinks.set(sink, enabled);
+        return (...args) => {
+            if (this.sinks.get(sink)) {
+                console.log(
+                    `%c[${sink}]`,
+                    "color: #8f3f71; font-weight: bold;",
+                    ...args
+                );
+            }
+        };
+    },
+    enableSink(sink) {
+        this.sinks.set(sink, true);
+    },
+    disableSink(sink) {
+        this.sinks.set(sink, false);
+    }
+};

frontend/src/main.js

@@ -1,6 +1,12 @@
 import App from './components/App.svelte';
 import gateway from './gateway';
 import { initStorageDefaults } from './storage';
+import logging from "./logging";
+
+window.__waffle = {
+	logging,
+	gateway
+};
 
 initStorageDefaults();
 gateway.init();

frontend/src/stores.js

@@ -1,8 +1,11 @@
 import { writable } from "svelte/store";
 import gateway, { GatewayEventType } from "./gateway";
+import logging from "./logging";
 import request from "./request";
 import { apiRoute } from "./storage";
 
+const storeLog = logging.logger("Store");
+
 class Store {
     constructor(value=null) {
         this._handlers = [];
@@ -13,14 +16,14 @@ class Store {
         const newLength = this._handlers.push(handler);
         const handlerIndex = newLength - 1;
         handler(this.value);
-        console.log(this.value);
+        storeLog("Subscription initialized with value", this.value);
         return () => {
             this._handlers.splice(handlerIndex, 1);
         };
     }
 
     updated() {
-        console.log(this.value);
+        storeLog(`updated(): calling ${this._handlers.length} handlers - value changed`, this.value);
         this._handlers.forEach(e => {
             e(this.value);
         });