Exceptions in when callbacks are transformed into rejections.

CHANGES

@@ -10,6 +10,11 @@ Deprecations:
     Mark Miller in a style where TitleCase is reserved for
     constructors.
 
+Next minor release
+ - Exceptions thrown in the callbacks of a `when` call
+   are now consumed, warned, and transformed into
+   rejections of the promise returned by `when`.
+
 0.2.7
  - Fixed a minor bug in thenable assimilation, regressed
    because of the change in the forwarding protocol.

lib/q.js

@@ -74,6 +74,10 @@ var create = Object.create || function create(prototype) {
     return new Type();
 }
 
+var print = typeof console === "undefined" ? identity : function (message) {
+    console.log(message);
+};
+
 /**
  * Performs a task in a future turn of the event loop.
  * @param {Function} task
@@ -355,16 +359,35 @@ function when(value, resolved, rejected) {
     var deferred = defer();
     var done = false;   // ensure the untrusted promise makes at most a
                         // single call to one of the callbacks
+
+    function _resolved(value) {
+        try {
+            return resolved ? resolved(value) : value;
+        } catch (exception) {
+            print(exception && exception.stack || exception);
+            return reject(exception);
+        }
+    }
+
+    function _rejected(reason) {
+        try {
+            return rejected ? rejected(reason) : reject(reason);
+        } catch (exception) {
+            print(exception && exception.stack || exception);
+            return reject(exception);
+        }
+    }
+
     forward(ref(value), "when", function (value) {
         if (done)
             return;
         done = true;
-        deferred.resolve(ref(value)[DUCK]("when", resolved, rejected));
+        deferred.resolve(ref(value)[DUCK]("when", _resolved, _rejected));
     }, function (reason) {
         if (done)
             return;
         done = true;
-        deferred.resolve(rejected ? rejected(reason) : reject(reason));
+        deferred.resolve(_rejected(reason));
     });
     return deferred.promise;
 }