Even just JavaScript Web Workers can be really helpful for doing heavy compute outside of the UI thread. JavaScript is pretty fast, it just needs to be unblocked. I used them once to sort a six-digit array of objects client side, while keeping the UI snappy (it took a couple seconds to process, but the UI was responsive the whole time)
Of course for some tasks you'll still need more than that, which very well may have been true for the OP, but benchmarking is good etc
Of course for some tasks you'll still need more than that, which very well may have been true for the OP, but benchmarking is good etc