clean(index, prefetch): move connection logic to prefetcher

Author: addyosmani

src/index.mjs

@@ -58,16 +58,6 @@ function extractInViewportLinks(el) {
 export default function (options) {
   options = options || { priority: 'low' };
   requestIdleCallback(() => {
-    if ('connection' in navigator) {
-      // Don't prefetch if the user is on 2G..
-      if (navigator.connection.effectiveType && /\slow-2g|2g/.test(navigator.connection.effectiveType)) {
-        return;
-      }
-      // Don't prefetch if Save-Data is enabled..
-      if (navigator.connection.saveData) {
-        return;
-      }
-    }
     // Prefetch an array of URLs if supplied (as an override)
     if (options.urls !== undefined && options.urls.length > 0) {
       prefetchLinks(options.urls, options.priority);

src/prefetch.mjs

@@ -83,13 +83,29 @@ const preFetched = {};
 
 const prefetch = function (url, priority) {
   return new Promise(resolve => {
+    if ('connection' in navigator) {
+      // Don't prefetch if the user is on 2G..
+      if (navigator.connection.effectiveType && /\slow-2g|2g/.test(navigator.connection.effectiveType)) {
+        resolve();
+        return;
+      }
+      // Don't prefetch if Save-Data is enabled..
+      if (navigator.connection.saveData) {
+        resolve();
+        return;
+      }
+    }
     if (preFetched[url]) {
       resolve();
       return;
     }
-
     if (priority && priority === `high`) {
-      highPriFetchStrategy(url);
+      highPriFetchStrategy(url)
+          .then(() => {
+            resolve();
+            preFetched[url] = true;
+          })
+          .catch(() => { });
     } else {
       supportedPrefetchStrategy(url)
           .then(() => {