js string from wasm

index.js

import { readFile } from 'node:fs/promises'

const wasm = await WebAssembly.instantiate(await readFile('main.wasm'), {}, { builtins: [ "js-string" ] })
  .then(n => n.instance.exports)

console.log(wasm.hello())

main.wat

(module
	;; type definition needed, incorrect signature error if you do `arrayref` inline
	(type $str_arr_t (array (mut i16)))
	(import "wasm:js-string" "fromCharCodeArray" (
		;; `externref` gets a signature error because it's an alias for `(ref null extern)`
		func $js_str (param (ref null $str_arr_t) i32 i32) (result (ref extern))
	))
	;; "hello from wasm!" in utf-16
	(data $str "h\00e\00l\00l\00o\00 \00f\00r\00o\00m\00 \00w\00a\00s\00m\00!\00\00\00")
	(func (export "hello") (result (ref extern))
		;; push a new array onto the stack of type `str_arr_t` with the data `$str`, offset of 0, length of 16 (bytes get calculated automatically)
		(array.new_data $str_arr_t $str (i32.const 0) (i32.const 16))
		(call $js_str (i32.const 0) (i32.const 16))
	)
)