Seems that the pretty print button disappears for some javascripts.
Reproduce:
load https://reactjs.org/, and in Debugger pannel, select app-[hash].js. You will see that there is no “{}” button at bottom of the source pannel.
Screenshot:
But if you load https://jquery.com/. and select the main.js. You will see the “{}” at the bottom.
I wonder why is that.