Help With Creating A Simple Glitch Chat Bot

I’m creating a chat bot as shown on the ‘https://dev.twitch.tv/docs/irc’ website, but I’d like to add some stuff to it. I’d like to add the ability to call out the specific user who types “!d20” and say something like
‘You rolled a ${num}. Grats. ${user}’. How would I go about getting the username of the person who sent a message? I am extremely confused as there are functions such as “function onMessageHandler(target, context, msg, self)” that show parameters but never shows the actual arguments put in. If anything, I’d just like to know where I can grab more information besides just target, context, msg, or self.

The example show on that page uses the TMI.js library, you’ll need to refer to the TMI.js documentation for help with that