createUuid () {
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
      const r = Math.random() * 16 | 0; const v = c === 'x' ? r : (r & 0x3 | 0x8)
      return v.toString(16)
    }
    )
  }
Creates and returns a RFC4122 version 4 compliant unique id.

@returns {string} A GUID.
@see https://stackoverflow.com/a/2117523