[teacup50]

You'd think this would be obvious. It's an inefficient and poorly designed "bytecode":

- The only number representation available is floating point.

- Concurrency is impossible except for the nearly useless web workers API; this prevents a language author from exposing any other type of concurrency mechanism.

- Anyone wishing to implement the "byte code" specification must implement or integrate a full Javascript parser and runtime.

[RussianCow]

On top of that, you have no control over memory management (which makes properly implementing lots of languages impossible).