code: function camelCase(string) {
    if (typeof string !== 'string') {
      throw new TypeError('First argument must be a string');
    }
  
    // custom property or no hyphen found
    if (CUSTOM_PROPERTY_OR_NO_HYPHEN_REGEX.test(string)) {
      return string;
    }
  
    // convert to camelCase
    return string
      .toLowerCase()
      .replace(hyphenPatternRegex, function(_, character) {
        return character.toUpperCase();
      });
  }
docs: Converts a string to camelCase.
  
  @param  {String} string - The string.
  @return {String}