How to compress Javascript files bundled in a custom skin into a single file that is available to all of the portlets in EPP 5?

Issue

The portal's skinning mechanism automatically compresses the css resources into a single file after creating a custom skin.

• Is there any way to achieve the same for the javascript resources?

• Is there a way to get a single compressed (merged) js file for all the javascript resources in the custom skin and at the same time get individual resources if running on dev mode?