Currently, the web app builder requires the existence of either an ArcGIS Online or Portal application in order to be used for the configuration of the web app. All maps accessed in the web app builder needs to be a web map inside Online or Portal. Some organizations are not ready to implement this product yet, but are very interested in implementing a JavaScript app. We're unable to use the Web AppBuilder for this in such situations and would have to do a fully customised JavaScript app. However, we will not be able to leverage on the framework and future widgets that comes with the Web AppBuilder in the customised JS app.