I meant more like storing closures to be used later after any locals are out of the stack frame, but tbh that's an abstraction that also causes allocations in C++ and Rust. On the other hand, no idea how JS internals work but I know in python getting the length of an array takes five layers of pointer indirection so it very well could be pointer to closure object -> pointer to list of closed variables -> pointer to boxed variable -> pointer to number or some ridiculous thing like that.

In C++, lambda functions don't require dynamic memory allocations, only type erasure via std::function does (if the capture list is too large for small-functiom-optimization)

However, C++ lambdas don't keep the parent evironment alive, so if you capture a local variable by reference and call the lambda outside the original function environment, you have a dangling reference and get a crash.

JavaScript is almost always JIT’ed and Python is usually not, so I wouldn’t rely on your Python intuition when talking about JavaScript performance. Especially when you’re using it to suggest that JavaScript programmers don’t understand the performance characteristics of their code.