First go to this link. Link: (https://ftp.mozilla.org/pub/firefox/releases/64.0/jsshell/) Download according to your operating system. Unzip the downloaded file and put it inside a folder. The js file in which I write the code, the js file must be inside my same folder.
When unzipped, clicking js.exe from inside the folder will open a command prompt. At this command prompt we will take user input. I must load and bring the file before taking user input. Here is the name of my JS file ab.js. Example: load('ab.js') This way I have to load the file every time I take input.