As developer Artem Govorov explains, Quokka, a free, "live scratchpad" add-in for Visual Studio Code, is aimed at coders who want to quickly try things out without leaving the comfort of their IDE:
Sometimes, you just need some isolated space for a small prototype that may end up being a foundation for a great invention. Sometimes you keep forgetting how a certain library function works, so just want to call it and inspect the output. Sometimes you want a playground to experiment with a new language feature or framework, to learn it or to teach it to others.
The animated GIF below does a good job of illustrating Quokka's benefits.