throw: Wasm exception handling instruction

(module
  ;; Import the error tag from JS
  (tag $my_error (import "env" "my_error") (param i32))

  (func $might_throw (param $value i32)
    ;; If value is negative, run the if block
    (local.get $value)
    (i32.const 0)
    (i32.lt_s)
    (if
      (then
        ;; Push the error code onto the stack, then throw an exception
        (i32.const 42)        ;; error code payload
        (throw $my_error)     ;; throw with the tag
      )
    )
  )
  (export "might_throw" (func $might_throw))
)

// Define error tag in JS
const myErrorTag = new WebAssembly.Tag({ parameters: ["i32"] });

// Import the tag into the module
const env = {
  my_error: myErrorTag,
};

WebAssembly.instantiateStreaming(fetch("{%wasm-url%}"), { env }).then(
  (result) => {
    try {
      // Negative value causes function to throw
      result.instance.exports.might_throw(-1);
    } catch (e) {
      if (e instanceof WebAssembly.Exception && e.is(myErrorTag)) {
        // 0 is the first payload value, which is equal to 42
        const errorCode = e.getArg(myErrorTag, 0);
        console.log("Error code:", errorCode);
      } else {
        // Throw other errors
        throw e;
      }
    }
  },
);