WebAssembly Set/Get String - https://wasdk.github.io/WasmFiddle/

main.c

char a[20];

void setA(char  b){
  *a=b;
}
char getA(){
  return *a;
}
int main() { 
setA("atest");
}

wasm.js

function setMemory(bytes, ptr, len) {
    const buffer = new Uint8Array(exports.memory.buffer, ptr, len)
    buffer.set(bytes);
}
var wasmModule = new WebAssembly.Module(wasmCode);
var wasmInstance = new WebAssembly.Instance(wasmModule, wasmImports);
var exports = wasmInstance.exports;
exports.main();
//Set
const encoder = new TextEncoder();
const bytes = encoder.encode("Hello World!");
const ptr = exports.getA();
setMemory(bytes, ptr, bytes.byteLength);
//Set

exports.setA(ptr + 1);
//Get
const array = new Uint8Array(exports.memory.buffer, exports.getA(), 20)
const decoder = new TextDecoder()
const string = decoder.decode(array)
//Get
log(string) console.log(exports.memory)