WebAssembly is not a bytecode for the web (quora.com)

WebAssembly is a compressed binary encoding of an AST. Bytecodes are for instruction sets. This has significant differences.

1) Loading an AST is much faster than parsing code and compiling it into an AST.

2) ASTs often go through optimization passes before being compiled to native assembly. Many of these steps can now happen at compile time instead of "parse" time.

3) ASTs are easier to target for language designers than bytecodes.