code: function combineClassNames(...classNames) {
    return classNames.map((value) => {
      if (!value) {
        return value;
      }
  
      return Array.isArray(value) ?
        combineClassNames.apply(void 0, value) :
        value;
    }).join(` `).replace(/ +/g, ` `).trim();
  }
docs: Returns a trimmed string of the combined class names.
  Class names can be either strings or arrays of strings.
  
  Example:
  
  combineClassNames(`my-class`, `my-other-class`, [`first`, `second`])
  // `myclass my-other-class first second`
  
  Arrays can be nested.
  @param {Array|String} classNames Any number of arguments of class names.
  @returns {String} The combined class names.