Service-worker-based prefetch

src/common.js

@@ -0,0 +1,8 @@
+export const ignorePaths = [
+    "/isso",
+    "/infipage",
+    "/wsthing",
+    "/random-stuff",
+    "/radio",
+    "/ystat"
+]

src/index.js

@@ -374,6 +374,19 @@ const compilePageJSTask = async () => {
     })
 }
 
+const compileServiceWorkerJSTask = async () => {
+    await esbuild.build({
+        entryPoints: [ path.join(srcDir, "sw.js") ],
+        bundle: true,
+        outfile: path.join(outDir, "sw.js"),
+        minify: true,
+        sourcemap: true,
+        define: {
+            "siteVersion": JSON.stringify(globalData.buildID)
+        }
+    })
+}
+
 const genServiceWorker = async () => {
     const serviceWorker = mustache.render(await readFile(path.join(assetsDir, "sw.js")), globalData)
     await minifyJSFile(serviceWorker, "sw.js", path.join(outDir, "sw.js"))
@@ -440,7 +453,7 @@ const tasks = {
     manifest: { deps: ["assetsDir"], fn: genManifest },
     minifyJS: { deps: ["assetsDir"], fn: minifyJSTask },
     compilePageJS: { deps: ["assetsDir"], fn: compilePageJSTask },
-    serviceWorker: { deps: [], fn: genServiceWorker },
+    serviceWorker: { deps: [], fn: compileServiceWorkerJSTask },
     images: { deps: ["assetsDir"], fn: doImages },
     offlinePage: { deps: ["assetsDir", "pagedeps"], fn: () => applyTemplate(globalData.templates.experiment, path.join(assetsDir, "offline.html"), () => path.join(outAssets, "offline.html"), {}) },
     assets: { deps: ["manifest", "minifyJS", "serviceWorker", "images", "compilePageJS"] },

src/page.js

@@ -1,22 +1,46 @@
 const idb = require("idb")
 const { solve } = require("yalps")
+const { ignorePaths } = require("./common")
+
+const prefetchHook = () => {
+    let lastFetch = 0
+    const prefetch = event => {
+        if (Date.now() - lastFetch >= 200) {
+            const href = new URL(event.target.getAttribute("href"), window.location)
+            if (href.origin === window.location.origin) {
+                for (const ignorePath of ignorePaths) {
+                    if (href.pathname.startsWith(ignorePath)) return
+                }
+                console.log("prefetch", href.href)
+                fetch(href)
+                lastFetch = Date.now()
+            }
+        }
+    }
+
+    for (const node of document.querySelectorAll("a[href]")) {
+        node.addEventListener("touchstart", prefetch)
+        node.addEventListener("mouseover", prefetch)
+    }
+}
 
 // attempt to register service worker
 if ("serviceWorker" in navigator) {
     navigator.serviceWorker.register("/sw.js", { scope: "/" }).then(reg => {
         if (reg.installing) {
-            console.log("Service worker installing");
+            console.log("Service worker installing")
         } else if (reg.waiting) {
-            console.log("Service worker installed");
+            console.log("Service worker installed")
         } else if (reg.active) {
-            console.log("Service worker active");
+            console.log("Service worker active")
+            prefetchHook()
         }
     }).catch(error => {
         // registration failed
-        console.log("Registration failed with " + error);
+        console.log("Registration failed with " + error)
     });
 } else {
-    console.log("Service workers are not supported.");
+    console.log("Service workers are not supported.")
 }
 
 // https://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript

src/sw.js

@@ -1,4 +1,5 @@
-const siteVersion = "{{buildID}}"
+import { ignorePaths } from "./common"
+
 const offlinePage = "/assets/offline.html"
 const cacheName = `${siteVersion}-v1`
 const precache = [
@@ -33,15 +34,6 @@ self.addEventListener("activate", event => {
     )
 })
 
-const ignorePaths = [
-    "/isso",
-    "/infipage",
-    "/wsthing",
-    "/random-stuff",
-    "/radio",
-    "/ystat"
-]
-
 const shouldRespond = req => {
     if (req.method !== "GET") { return false } // do not respond to non-GET requests
     if (!req.url.startsWith(self.location.origin)) { return false } // do not respond to cross-origin requests