The difference is in the surface area of the standard library -- Java applets exposed a lot of stuff that turned out to have a lot of security holes, and it was basically impossible to guarantee there weren't further holes. In WASM, the linear memory and very simple OS interface makes the sandboxing much more tractable.
What I’m thinking of is simply memory corruption issues from the linear memory model, and while these can only corrupt the given process, not anything outside, it is still not something the JVM allows.
Wasm GC also introduces non-null reference types, and the validation algorithm guarantees that locals of declared non-null type cannot be used before being initialized. That's also done as part of the single-pass verification.
Wasm GC has a lower-level object model and type system than the JVM (basically structs, arrays, and first-class functions, to which object models are lowered), so it's possible that a higher-level type system, when lowered to Wasm GC, may not be enforceable at the bytecode level. So you could, e.g. screw up the virtual dispatch sequence of a Java method call and end up with a Wasm runtime type error.
> Two’s complement signed integers in 32 bits and optionally 64 bits.
https://webassembly.org/docs/portability/#assumptions-for-ef...
And nothing suggesting unsigned ints here:
With the two's complement convention, the concept of 'signedness' only matters when a narrow integer value needs to be extended to a wider value (e.g. 8-bit to 16-bit), specifically whether the new bits needs to be replicated from the narrow value's topmost bit (for signed extension) or set to zero (for unsigned extension).
It would be interesting to speculate what a high level language would look like with such sign-agnostic "Schroedinger's integer types").
https://webassembly.github.io/spec/core/appendix/index-instr...
See how there's only i32.load and i32.eq, but there's i32.lt_u and i32.lt_s. Loading bits from memory or comparing them is the same operation bit for bit for each of signed and unsigned. However, less than requires knowing the desired signess, and is split between signed and unsigned.
