Script to center text vertically in adobe illustrator?

Or you may be content with double clicking here

to trim excess unused height from your text container. I added a descender so you can see how  important this is to consider.

If you goal is to get the type in the center of the text box, that is not possibly in Illustraro as in InDesign.

You can have the align palette to do this, but you need to do 2 things

1. Add an effect >>Path >>  outline Object to your tyep element
2. Turn on use preview bounds

The reason the align palette does not by default center text, is that it is centering upon the font (including the space above and below the ascenders and descenders, coded into the font. 

Not sure if this helps you, but please clarify or provide an example with more detail of what your end result you are looking to do.

The script would have to calculate something such as a baseline shift, and you would need to let us know what you want to do about ascenders and descender.

Might be better to post here, or I can move your post for you

Illustrator Scripting

There are ways to do this without scripting, of which will add a separate reply.