Error thrown in xhr.onreadystatechange when javascript execution is suspended/resumed on iOS

src/ng/httpBackend.js

@@ -83,6 +83,11 @@ function createHttpBackend($browser, createXhr, $browserDefer, callbacks, rawDoc
         // we can't set xhr.onreadystatechange to undefined or delete it because that breaks IE8 (method=PATCH) and
         // Safari respectively.
         if (xhr && xhr.readyState == 4) {
+          // onreadystatechange might by called multiple times
+          // with readyState === 4 on mobile webkit caused by
+          // xhrs that are resolved while the app is in the background (see #5426).
+          xhr.onreadystatechange = function(){};
+
           var responseHeaders = null,
               response = null;
 

test/ng/httpBackendSpec.js

@@ -90,6 +90,24 @@ describe('$httpBackend', function() {
     expect(callback).toHaveBeenCalledOnce();
   });
 
+  // onreadystatechange might by called multiple times
+  // with readyState === 4 on mobile webkit caused by
+  // xhrs that are resolved while the app is in the background (see #5426).
+  it('should remove onreadystatechange when it is called with readyState=4 to ignore multiple calls', function() {
+    $backend('GET', 'URL', null, callback);
+    xhr = MockXhr.$$lastInstance;
+
+    xhr.status = 200;
+    xhr.readyState = 4;
+
+    var orig = xhr.onreadystatechange
+
+    xhr.onreadystatechange();
+    expect(xhr.onreadystatechange).toNotBe(orig);
+
+    xhr.onreadystatechange(); // empty function
+  });
+
   // onreadystatechange might by called multiple times
   // with readyState === 4 on mobile webkit caused by
   // xhrs that are resolved while the app is in the background (see #5426).