$ sudo apt-get update
$ sudo apt-get install libjs-class.js 

libjs-class.js is installed in your system.

Make ensure the libjs-class.js package were installed using the commands given below,

$ sudo dpkg-query -l | grep libjs-class.js *

You will get with libjs-class.js package name, version, architecture and description in a table

libjs-class.js package basic information: