The main differences are probably the compilers involved, which tend to be layered based on how often a routine gets called (starting interpreted, then using a

The main differences are probably the compilers involved, which tend to be layered based on how often a routine gets called (starting interpreted, then using a fast-but-dumb JIT compiler, then a slow-but-smart JIT compiler). There are many JVMs, each operating slightly differently, but the HotSpot JIT seems to be the most widely used (e.g. https://cl4es.github.io/2019/11/20/OpenJDK-Startup-Update.html https://cl4es.github.io/2019/11/20/OpenJDK-Startup-Update.ht... ) Node runs on V8, which is described in more detail at https://v8.dev/blog/ignition-interpreter https://v8.dev/blog/ignition-interpreter Another big diffence is that Java does lots of special handling for classes, e.g. hooking up 'reflection' machinery, allowing dynamic 'class loaders', etc. which happens during an application's startup. In contrast, Javascript 'classes' are basically just functions (constructors); and Javascript functions are values just like anything else; hence there's less of an up-front cost to JS code. Python works in pretty much the same way from a language level (but its CPython interpreter works very differently to V8).