How to make Vim detect filetype from the shebang line?

Following the instructions listed in :help new-filetype-scripts,
create the scripts.vim file in the user runtime directory (~/.vim/
on Unix-like systems), and write the following script in it:

if did_filetype()
    finish
endif
if getline(1) =~# '^#!.*/bin/env\s\+node\>'
    setfiletype javascript
endif