code: function _isFile (file, callback) {
  
  			if ("undefined" === typeof file) {
  				throw new ReferenceError("missing \"file\" argument");
  			}
  				else if ("string" !== typeof file) {
  					throw new TypeError("\"file\" argument is not a string");
  				}
  				else if ("" === file.trim()) {
  					throw new Error("\"file\" argument is empty");
  				}
  			else if ("undefined" === typeof callback) {
  				throw new ReferenceError("missing \"callback\" argument");
  			}
  				else if ("function" !== typeof callback) {
  					throw new TypeError("\"callback\" argument is not a function");
  				}
  			else {
  
  				lstat(file, (err, stats) => {
  					return callback(null, Boolean(!err && stats.isFile()));
  				});
  
  			}
  
  		}
docs: methods 
  Async isFile
  @param {string} file : file to check
  @param {function} callback : operation's result
  @returns {void}