fix #593, only call removeAttribute when have the method

lib/browser/property-descriptor.ts

@@ -56,6 +56,8 @@ function canPatchViaPropertyDescriptor() {
     if (desc && !desc.configurable) return false;
   }
 
+  const xhrDesc = Object.getOwnPropertyDescriptor(XMLHttpRequest.prototype, 'onreadystatechange');
+
   // add enumerable and configurable here because in opera
   // by default XMLHttpRequest.prototype.onreadystatechange is undefined
   // without adding enumerable and configurable will cause onreadystatechange
@@ -69,7 +71,8 @@ function canPatchViaPropertyDescriptor() {
   });
   const req = new XMLHttpRequest();
   const result = !!req.onreadystatechange;
-  Object.defineProperty(XMLHttpRequest.prototype, 'onreadystatechange', {});
+  // restore original desc
+  Object.defineProperty(XMLHttpRequest.prototype, 'onreadystatechange', xhrDesc || {});
   return result;
 };
 

lib/common/utils.ts

@@ -108,7 +108,9 @@ export function patchProperty(obj, prop) {
         r = oriDesc.get.apply(this, arguments);
         if (r) {
           desc.set.apply(this, [r]);
-          this.removeAttribute(prop);
+          if (typeof this['removeAttribute'] === 'function') {
+            this.removeAttribute(prop);
+          }
         }
       }
     }

test/browser/XMLHttpRequest.spec.ts

@@ -209,4 +209,15 @@ describe('XMLHttpRequest', function() {
          });
        });
      });
+
+  it('should not throw error when get XMLHttpRequest.prototype.onreadystatechange the first time',
+     function() {
+       const func = function() {
+         testZone.run(function() {
+           const req = new XMLHttpRequest();
+           req.onreadystatechange;
+         });
+       };
+       expect(func).not.toThrow();
+     });
 });