fix($browser.xhr): fix IE6, IE7 bug - sync xhr when serving from cache

IE6, IE7 is sync when serving content from cache.
We want consistent api, so we have to use setTimeout to make it async.

src/service/browser.js

@@ -73,6 +73,11 @@ function Browser(window, document, body, XHR, $log, $sniffer) {
     }
   }
 
+  // normalize IE bug (http://bugs.jquery.com/ticket/1450)
+  function fixStatus(status) {
+    return status == 1223 ? 204 : status;
+  }
+
   /**
    * @ngdoc method
    * @name angular.module.ng.$browser#xhr
@@ -120,14 +125,22 @@ function Browser(window, document, body, XHR, $log, $sniffer) {
       forEach(headers, function(value, key) {
           if (value) xhr.setRequestHeader(key, value);
       });
-      xhr.onreadystatechange = function() {
-        if (xhr.readyState == 4) {
-          // normalize IE bug (http://bugs.jquery.com/ticket/1450)
-          var status = xhr.status == 1223 ? 204 : xhr.status;
-          completeOutstandingRequest(callback, status, xhr.responseText);
-        }
-      };
+
       xhr.send(post || '');
+
+      // IE6, IE7 bug - does sync when serving from cache
+      if (xhr.readyState == 4) {
+        setTimeout(function() {
+          completeOutstandingRequest(callback, fixStatus(xhr.status), xhr.responseText);
+        }, 0);
+      } else {
+        xhr.onreadystatechange = function() {
+          if (xhr.readyState == 4) {
+            completeOutstandingRequest(callback, fixStatus(xhr.status), xhr.responseText);
+          }
+        };
+      }
+
       return xhr;
     }
   };

test/service/browserSpecs.js

@@ -227,6 +227,35 @@ describe('browser', function() {
     it('should return raw xhr object', function() {
       expect(browser.xhr('GET', '/url', null, noop)).toBe(xhr);
     });
+
+    it('should be async even if xhr.send() is sync', function() {
+      // IE6, IE7 is sync when serving from cache
+      var xhr;
+      function FakeXhr() {
+        xhr = this;
+        this.open = this.setRequestHeader = noop;
+        this.send = function() {
+          this.status = 200;
+          this.responseText = 'response';
+          this.readyState = 4;
+        };
+      }
+
+      var callback = jasmine.createSpy('done').andCallFake(function(status, response) {
+        expect(status).toBe(200);
+        expect(response).toBe('response');
+      });
+
+      browser = new Browser(fakeWindow, jqLite(window.document), null, FakeXhr, null);
+      browser.xhr('GET', '/url', null, callback);
+      expect(callback).not.toHaveBeenCalled();
+
+      fakeWindow.setTimeout.flush();
+      expect(callback).toHaveBeenCalledOnce();
+
+      (xhr.onreadystatechange || noop)();
+      expect(callback).toHaveBeenCalledOnce();
+    });
   });
 
   describe('defer', function() {