I need to rename all files with .js extension, but names of files can vary, for example:

rootDirectory
--firstDirectory
----first.js
--secondFileDirectory
----second.js
--thirdDirectory
----third.js

Needs to be renamed to

rootDirectory
--firstDirectory
----newName.js
--secondFileDirectory
----newName.js
--thirdDirectory
----newName.js

Is there a way to do it?

I'm using Ubuntu 14.04