Most JavaScript security failures aren't exotic. They come from trusting the wrong boundary, executing the wrong string, or forgetting how much power the browser hands to whoever turns up.
Most React performance problems are really scheduling problems. A practical look at Fiber, reconciliation, and what actually happens after setState.
After enough profiling sessions you start to realise the language is rarely the bottleneck. Our assumptions usually are.
Modern JavaScript engines are astonishingly fast, but only because they spend most of their time pretending your code is better than it actually is.
Most explanations stop at the call stack and callback queue. The reality is more interesting, and explains many of the bugs engineers encounter in production.