I encountered the issue when trying to get the morph feature of Turbo 8 to work. The page just kept refreshing and I didn't understand why. There were no good tutorials yet so I had to dig into the gem.

First, I opened it with

bundle open turbo-rails

There is see that the gem has 3 javascript files:

app/assets/javascripts/turbo.js
app/assets/javascripts/turbo.min.js
app/assets/javascripts/turbo.min.js.map

I added some log statements in turbo.js but realized that I have to change the minified version turbo.min.js. For convenience, I changed the turbo.js file as it's easier to read and recompiled the min.js file with terser.

npm install terser -g

terser turbo.js -o turbo.min.js --compress --mangle 

After that I was able to add log statements to the gem's javascript and figure out the issue.

After you play with a gem don't forget to reset its code.