Validating a US (or international) phone number with Parsley and libphonenumber-js

ustel.html

<!-- requirements -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/parsley.js/2.6.2/parsley.min.js"></script>
<script src="https://halt-hammerzeit.github.io/libphonenumber-js/libphonenumber-js.min.js"></script>
  
<!-- custom validator -->
<script type="text/javascript">
$(document).ready(function() {
  window.Parsley.addValidator('ustel', {
    requirementType: 'string',
    validateString: function(value) {
      var parsed = libphonenumber.parse(value, 'US'); // Change 'US' if you must.
      if ('phone' in parsed){
        return true;
      } else {
        return false;
      }
    },
    messages: {
      en: 'Please enter a US phone number'
    }
  });
});
</script>