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

libjs-rtcninja is installed in your system.

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

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

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

libjs-rtcninja package basic information: