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

libjs-modestmaps is installed in your system.

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

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

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

libjs-modestmaps package basic information: