feat(promise): fix #955, print readable log when uncaught promise error

lib/common/promise.ts

@@ -6,6 +6,15 @@
  * found in the LICENSE file at https://angular.io/license
  */
 Zone.__load_patch('ZoneAwarePromise', (global: any, Zone: ZoneType, api: _ZonePrivate) => {
+  function readableObjectToString(obj: any) {
+    if (obj && obj.toString === Object.prototype.toString) {
+      const className = obj.constructor && obj.constructor.name;
+      return (className ? className : '') + ': ' + JSON.stringify(obj);
+    }
+
+    return obj ? obj.toString() : Object.prototype.toString.call(obj);
+  }
+
   interface UncaughtPromiseError extends Error {
     zone: AmbientZone;
     task: Task;
@@ -164,8 +173,9 @@ Zone.__load_patch('ZoneAwarePromise', (global: any, Zone: ZoneType, api: _ZonePr
         if (queue.length == 0 && state == REJECTED) {
           (promise as any)[symbolState] = REJECTED_NO_CATCH;
           try {
+            // try to print more readable error log
             throw new Error(
-                'Uncaught (in promise): ' + value +
+                'Uncaught (in promise): ' + readableObjectToString(value) +
                 (value && value.stack ? '\n' + value.stack : ''));
           } catch (err) {
             const error: UncaughtPromiseError = err;

test/common/Promise.spec.ts

@@ -33,6 +33,11 @@ function flushMicrotasks() {
   Zone.current.get('flush')();
 }
 
+class TestRejection {
+  prop1: string;
+  prop2: string;
+}
+
 describe(
     'Promise', ifEnvSupports('Promise', function() {
       if (!global.Promise) return;
@@ -344,6 +349,38 @@ describe(
               done();
             });
           });
+
+          it('should print readable information when throw a not error object', (done) => {
+            let promiseError: Error = null;
+            let zone: Zone = null;
+            let task: Task = null;
+            let rejectObj: TestRejection;
+            queueZone
+                .fork({
+                  name: 'promise-error',
+                  onHandleError: (delegate: ZoneDelegate, current: Zone, target: Zone, error: any):
+                                     boolean => {
+                                       promiseError = error;
+                                       delegate.handleError(target, error);
+                                       return false;
+                                     }
+                })
+                .run(() => {
+                  zone = Zone.current;
+                  task = Zone.currentTask;
+                  rejectObj = new TestRejection();
+                  rejectObj.prop1 = 'value1';
+                  rejectObj.prop2 = 'value2';
+                  Promise.reject(rejectObj);
+                  expect(promiseError).toBe(null);
+                });
+            setTimeout((): void => null);
+            setTimeout(() => {
+              expect(promiseError.message)
+                  .toMatch(/Uncaught \(in promise\):.*: {"prop1":"value1","prop2":"value2"}/);
+              done();
+            });
+          });
         });
 
         describe('Promise.race', () => {