$ sudo apt-get update
$ sudo apt-get install libjs-mootools 

libjs-mootools is installed in your system.

Make ensure the libjs-mootools package were installed using the commands given below,

$ sudo dpkg-query -l | grep libjs-mootools *

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

libjs-mootools package basic information: