code: function (value, prefix) {
          return angular.isString(value)  &&
            angular.isString(prefix) &&
            value.lastIndexOf(prefix, 0) === 0;
        }
docs: Checks if a string value starts with a given prefix.
  
  @param value the value
  @param prefix the prefix
  @returns {boolean} true if the given value starts with the given prefix.