habitica-self-host/common/script/libs/uuid.js

// TODO use node-uuid module
module.exports = function() {
  return "xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx".replace(/[xy]/g, function(c) {
    var r, v;
    r = Math.random() * 16 | 0;
    v = (c === "x" ? r : r & 0x3 | 0x8);
    return v.toString(16);
  });
};