code: function format(pathObject) {
      if (!isObject(pathObject)) {
        throw new TypeError('Parameter `pathObject` must be an object, not ' +
          typeof pathObject);
      }
  
      var root = pathObject.root || '';
  
      if (!isString(root)) {
        throw new TypeError('`pathObject.root` must be a string or undefined, not '  + 
          typeof pathObject.root);
      }
  
      var dir = pathObject.dir ? pathObject.dir + '/' : '';
      var base = pathObject.base || '';
      return dir + base;
    }
docs: format
  @param {Object} pathObject
  @return {String}