feat: assert that right ZoneAwarePromise is available (#420)

lib/zone.ts

@@ -232,6 +232,11 @@ interface ZoneType {
    * @returns {Task} The task associated with the current execution.
    */
   currentTask: Task;
+
+  /**
+   * Verify that Zone has been correctly patched. Specifically that Promise is zone aware.
+   */
+  assertZonePatched();
 }
 
 /**
@@ -508,6 +513,16 @@ const Zone: ZoneType = (function(global: any) {
   class Zone implements AmbientZone {
     static __symbol__: (name: string) => string = __symbol__;
 
+    static assertZonePatched() {
+      if (global.Promise !== ZoneAwarePromise) {
+        throw new Error("Zone.js has detected that ZoneAwarePromise `(window|global).Promise` " +
+            "has been overwritten.\n" +
+            "Most likely cause is that a Promise polyfill has been loaded " +
+            "after Zone.js (Polyfilling Promise api is not necessary when zone.js is loaded. " +
+            "If you must load one, do so before loading zone.js.)");
+      }
+    }
+
 
     static get current(): AmbientZone { return _currentZone; };
     static get currentTask(): Task { return _currentTask; };

test/common/zone.spec.ts

@@ -149,6 +149,27 @@ describe('Zone', function () {
         { microTask: false, macroTask: false, eventTask: false, change: 'microTask', zone: 'parent' },
       ]);
     });
+
+    describe('assert ZoneAwarePromise', () => {
+      it('should not throw when all is OK', () => {
+        Zone.assertZonePatched();
+      });
+
+      it('should throw when Promise has been patched', () => {
+        class WrongPromise{}
+
+        var ZoneAwarePromise = global.Promise;
+        global.Promise = WrongPromise;
+        try {
+          expect(ZoneAwarePromise).toBeTruthy();
+          expect(() => Zone.assertZonePatched()).toThrow();
+        } finally {
+          // restore it.
+          global.Promise = ZoneAwarePromise;
+        }
+        Zone.assertZonePatched();
+      });
+    });
   });
 
   describe('invoking tasks', () => {