In Javascript, how can I perform a global replace on string with a variable inside ‘/’ and ‘/g’?

var mystring = "hello world test world";
var find = "world";
var regex = new RegExp(find, "g");
alert(mystring.replace(regex, "yay")); // alerts "hello yay test yay"

In case you need this into a function

  replaceGlobally(original, searchTxt, replaceTxt) {
    const regex = new RegExp(searchTxt, 'g');
    return original.replace(regex, replaceTxt) ;
  }