This is a complete overhaul (API changes) from the 7.x-1.x branch. There is no "upgrade" path, modules will need to manually reconfigure their JS module integration. If a module breaks, please file an issue in their issue queue.
This release fixes an error that was caused by a recent design change and resulted in passing unexpected arguments to the callback function defined in hook_js(). It is highly recommended to update to this release if you recently installed the 6.x-1.2 release.