Indentation in Emacs

In the evening I read The Ultimate Guide To Indentation in Emacs (Tabs and Spaces). I am interested in this because I am working on a project that uses hard tabs in JavaScript but spaces in Perl source. And since the default tab width is 8 in my Emacs set up this makes for very wide lines in the former case.

What I currently use is changing Emacs's idea of the <TAB> character's length by evaluating the following Emacs Lisp code:

(setq-default tab-width 4)

But I am going to study the suggested configuration in the article mentioned above and most likely add it to my Emacs configuration.