From b8bd686d15c22753a69b4430d7ed324eea57a7d0 Mon Sep 17 00:00:00 2001
From: Lee Powell <lee@leepowell.co.uk>
Date: Thu, 21 May 2020 20:52:07 +0100
Subject: [PATCH 1/2] prefetch returns promise instead of undefined

---
 src/index.mjs | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/index.mjs b/src/index.mjs
index ccdb78af..0c0b8589 100644
--- a/src/index.mjs
+++ b/src/index.mjs
@@ -114,21 +114,26 @@ export function listen(options) {
 export function prefetch(url, isPriority, conn) {
   if (conn = navigator.connection) {
     // Don't prefetch if using 2G or if Save-Data is enabled.
-    if (conn.saveData || /2g/.test(conn.effectiveType)) return;
+    if (conn.saveData) {
+      return Promise.reject(new Error('Cannot prefetch, Save-Data is enabled'));
+    }
+    if (/2g/.test(conn.effectiveType)) {
+      return Promise.reject(new Error('Cannot prefetch, network conditions are poor'));
+    }
   }
 
   // Dev must supply own catch()
   return Promise.all(
-    [].concat(url).map(str => {
-      if (!toPrefetch.has(str)) {
-        // Add it now, regardless of its success
-        // ~> so that we don't repeat broken links
-        toPrefetch.add(str);
+      [].concat(url).map(str => {
+        if (!toPrefetch.has(str)) {
+          // Add it now, regardless of its success
+          // ~> so that we don't repeat broken links
+          toPrefetch.add(str);
 
-        return (isPriority ? priority : supported)(
-          new URL(str, location.href).toString()
-        );
-      }
-    })
+          return (isPriority ? priority : supported)(
+              new URL(str, location.href).toString()
+          );
+        }
+      })
   );
 }

From 2e8e4ea3ca7ea0f57b840c3d89314c309ea7b192 Mon Sep 17 00:00:00 2001
From: Lee Powell <lee@leepowell.co.uk>
Date: Thu, 21 May 2020 20:52:07 +0100
Subject: [PATCH 2/2] prefetch returns promise instead of undefined

---
 .vscode/settings.json | 7 +++++++
 src/chunks.mjs        | 9 +++++++--
 src/index.mjs         | 9 +++++++--
 3 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 .vscode/settings.json

diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 00000000..e7962eba
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,7 @@
+{
+  "editor.codeActionsOnSave": {
+    "source.fixAll.eslint": false,
+    "source.organizeImports": false
+  },
+  "editor.formatOnSave": true
+}
diff --git a/src/chunks.mjs b/src/chunks.mjs
index 5d617e43..fe849007 100644
--- a/src/chunks.mjs
+++ b/src/chunks.mjs
@@ -121,7 +121,12 @@ export function listen(options) {
 export function prefetch(url, isPriority, conn) {
   if (conn = navigator.connection) {
     // Don't prefetch if using 2G or if Save-Data is enabled.
-    if (conn.saveData || /2g/.test(conn.effectiveType)) return;
+    if (conn.saveData) {
+      return Promise.reject(new Error('Cannot prefetch, Save-Data is enabled'));
+    }
+    if (/2g/.test(conn.effectiveType)) {
+      return Promise.reject(new Error('Cannot prefetch, network conditions are poor'));
+    }
   }
 
   // Dev must supply own catch()
@@ -138,4 +143,4 @@ export function prefetch(url, isPriority, conn) {
       }
     })
   );
-}
\ No newline at end of file
+}
diff --git a/src/index.mjs b/src/index.mjs
index ccdb78af..4363cbcb 100644
--- a/src/index.mjs
+++ b/src/index.mjs
@@ -114,7 +114,12 @@ export function listen(options) {
 export function prefetch(url, isPriority, conn) {
   if (conn = navigator.connection) {
     // Don't prefetch if using 2G or if Save-Data is enabled.
-    if (conn.saveData || /2g/.test(conn.effectiveType)) return;
+    if (conn.saveData) {
+      return Promise.reject(new Error('Cannot prefetch, Save-Data is enabled'));
+    }
+    if (/2g/.test(conn.effectiveType)) {
+      return Promise.reject(new Error('Cannot prefetch, network conditions are poor'));
+    }
   }
 
   // Dev must supply own catch()
@@ -126,7 +131,7 @@ export function prefetch(url, isPriority, conn) {
         toPrefetch.add(str);
 
         return (isPriority ? priority : supported)(
-          new URL(str, location.href).toString()
+            new URL(str, location.href).toString()
         );
       }
     })