There are several important lessons to learn from the Java bytecode format and members of the WebAssembly (including myself) do have experience here. In particular, JVM class files would be a poor fit for WebAssembly because:
1. They impose Java's class and primitive type model.
2. They allow irreducible control flow.
3. They aren't very compact. Lots of redundancy in constant pools across classes and still a lot of possibility for compression.
4. Verification of JVM class files is an expensive operation requiring control and dataflow analysis (see stackmaps added in the Java 7 class file format for rationale).
5. No notion of low-level memory access. WebAssembly specifically addresses this, exposing the notion of a native heap that can be bit-banged directly by applications.
1. They impose Java's class and primitive type model. 2. They allow irreducible control flow. 3. They aren't very compact. Lots of redundancy in constant pools across classes and still a lot of possibility for compression. 4. Verification of JVM class files is an expensive operation requiring control and dataflow analysis (see stackmaps added in the Java 7 class file format for rationale). 5. No notion of low-level memory access. WebAssembly specifically addresses this, exposing the notion of a native heap that can be bit-banged directly by applications.