To be fair the AST structure can also be implemented more efficiently without better control over memory layout. The JS ecosystem standardized on polymorphic ASTs, which in retrospect seems dumb, but is not a result of any fundamental limitation in JS.

E.g. in ESTree evaluating such a common expression as `node.type` is actually really expensive -- it incurs the costs of a hashmap lookup (more or less) where you'd expect it to be able to be implemented using pointer arithmetic.

I get what you're saying but you've missed my point.

You're optimising your execution but there's trade-offs: you need to think about optimising your software development model holistically. There's little point in having the most efficient abandonware.

A JS tool may be technically suboptimal but that's not a problem unless AST size is a bottleneck.

> AST data structures can be implemented much more efficiently with better control over memory layout

I assume you're right but I'm not sure I fully understand why this is the case - can you give examples of how a data structure can be implemented in ways that aren't possible in JS?