UI is freezing, one of the CPU cores burning, you can do nothing at the moment. The only thing you can hear right now is the howl cooler. The single perception you can feel is hot as a hell metal case of the laptop. This is not a horror story or a thriller – this is a modern web app that runs everything in the main JS thread.
We should use the benefits of parallel computing to make the user feel like in a rainbow paradise instead of a nightmare. We have all the powers to execute the code in parallel and keep the main thread ready to interactions. With modern features like Web Workers, WebAssembly, and Worklets, this is not true anymore. I want to share the experience running jobs in parallel on real examples, that could be adapted to your requirements.