onValue(handler, [queueName])

Register an event handler on the Value-like object obj to trigger when its value changes. obj must implement @@can.onValue to be compatible with can-reflect.onKeyValue. The function passed as handler will receive the new value of obj as the first argument, and the previous value of obj as the second argument.

var obj = canCompute("foo");
canReflect.onValue(obj, function(newVal, oldVal) {
    console.log("compute is now", newVal, ", was", oldVal);
});

obj("bar");  // -> logs "compute is now bar , was foo"