unreachable

unreachable is used to denote a point in code that should not be reachable. unreachable is an unconditional trap: in the case where an unreachable is reached and executed, the instruction traps.

Try it

(module
  (func (export "throw")
    unreachable
  )
)

const url = "{%wasm-url%}";
await WebAssembly.instantiateStreaming(fetch(url)).then((result) => {
  result.instance.exports.throw();
  // Expected output: RuntimeError: unreachable
});

Syntax

wasm

unreachable

Instruction	Binary opcode
`unreachable`	`0x00`