An example of how you could use C++ in JS with cpp-loader, and webpack's first class WASM support.

_entry.js

import("./abc.js").then(abc => abc.doIt()); 

abc.js

import { duplicateText } from "./string.cpp";

export function doIt() {
  console.log(duplicateText(“Hello World”));
}

string.cpp

extern"C" const char* duplicateText(const char* text) {
  int len = strlen(text);
  char* newstr = new char[len*2 + 1];
  strcpy(newstr, text);
  strcat(newstr, text);
  return newstr;
}