mouse drag function in javascript

I am not familiar with javascript coding to deal with the problem of the source code on my own.
I downloaded a nice Linkage Simulator code written in Javascript from this website https://edu-mat.sakuraweb.com/linksim/index_en.html. Please go down to Download and click on icon download system. You will get linksys_1.01.zip file. Unzip it to get javascript code on your computer.
The problem is dragging the parts on the screen. When I run Linksys from their website, the dragging of the mechanical parts on the screen with you mouse icon works fine.
When I run javascript code from my PC, the code runs fine except when I try drag mechanical parts with my mouse. The parts are stuck. Obviously, the mouse function for dragging the parts is disabled. How do I enable it?
Thank you for your time.