Return a Promise when no callback is provided for a function call

This returns a Promise if Promise is supported and no callback
is provided.  The Promise resolves when the function call succeeds,
or rejects when it fails.

Change-Id: I529f5c2c0ff8997820f3d1b4d4b364cd8521e9b5
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>

2 files changed, 26 insertions, 1 deletions

diff --git a/examples/webchannel/shared/qwebchannel.js b/examples/webchannel/shared/qwebchannel.js
index 6cc3690..fca45d9 100644
--- a/examples/webchannel/shared/qwebchannel.js
+++ b/examples/webchannel/shared/qwebchannel.js
@@ -346,6 +346,7 @@ function QObject(name, data, webChannel)
         object[methodName] = function() {
             var args = [];
             var callback;
+            var errCallback;
             for (var i = 0; i < arguments.length; ++i) {
                 var argument = arguments[i];
                 if (typeof argument === "function")
@@ -358,6 +359,17 @@ function QObject(name, data, webChannel)
                     args.push(argument);
             }
 
+            var result;
+            // during test, webChannel.exec synchronously calls the callback
+            // therefore, the promise must be constucted before calling
+            // webChannel.exec to ensure the callback is set up
+            if (!callback && (typeof(Promise) === 'function')) {
+              result = new Promise(function(resolve, reject) {
+                callback = resolve;
+                errCallback = reject;
+              });
+            }
+
             webChannel.exec({
                 "type": QWebChannelMessageTypes.invokeMethod,
                 "object": object.__id__,
@@ -369,8 +381,12 @@ function QObject(name, data, webChannel)
                     if (callback) {
                         (callback)(result);
                     }
+                } else if (errCallback) {
+                  (errCallback)();
                 }
             });
+
+            return result;
         };
     }
 
diff --git a/tests/auto/qml/tst_webchannel.qml b/tests/auto/qml/tst_webchannel.qml
index b0f3263..ed1c4a1 100644
--- a/tests/auto/qml/tst_webchannel.qml
+++ b/tests/auto/qml/tst_webchannel.qml
@@ -87,6 +87,7 @@ TestCase {
             property var myProperty : 0
             function myMethod(arg) {
                 lastMethodArg = arg;
+                return myProperty;
             }
             signal mySignal(var arg1, var arg2)
         }
@@ -238,6 +239,7 @@ TestCase {
         var testObjBeforeDeletion;
         var testObjAfterDeletion;
         var testObjId;
+        var testReturn;
         var channel = client.createChannel(function(channel) {
             channel.objects.myFactory.create("testObj", function(obj) {
                 testObjId = obj.__id__;
@@ -249,7 +251,9 @@ TestCase {
                     testObjAfterDeletion = obj;
                 });
                 obj.myProperty = 42;
-                obj.myMethod("foobar");
+                obj.myMethod("foobar").then(function(result) {
+                    testReturn = result;
+                });
             });
         });
         client.awaitInit();
@@ -288,6 +292,11 @@ TestCase {
         // the server should eventually notify the client about the property update
         client.awaitPropertyUpdate();
 
+        // check that the Promise from myMethod was resolved
+        // must happen after waiting for something so the Promise callback
+        // can execute
+        compare(testReturn, 42);
+
         client.awaitIdle();
 
         // property should be wrapped