JS BigInt ↔ Wasm i64

Modern JS engines map Wasm i64 to JavaScript BigInt. You can pass BigInt values to Wasm functions that take i64 and receive BigInt from i64 results.

(module
  (func (export "inc64") (param $x i64) (result i64)
    (i64.add (local.get $x) (i64.const 1)))
)

From JS, pass and receive BigInt:

const { instance } = await WebAssembly.instantiate(wasmBytes);
console.log(instance.exports.inc64(41n)); // 42n

• Non-BigInt JS numbers are not accepted for i64 parameters.
• Passing BigInt to non-i64 params will throw.

Instruction Reference

• i64 Instructions