function () {function () {function () {function () {//pass}}}
}

var path = './async.txt';
// check if async.txt exists
fs.stat(path, function (err, stats) {if (err)return errif (stats == undefined) {fs.readFile(__filename, function (err, content) {if (err)return errvar code = content.toString();fs.writeFile(path, code, function (err) {if (err)return errconsole.log('async.txt created!');});});}
});

function start (path,filePath){stats(path,function(err,stat){if (err)                       return err;        else if(stat == undefined){reads(filePath,function(err,data){if (err)return err;var code = data.toString();writes(code,function(err,result){if (err)return errconsole.log('async.txt created!');})                })}})
}function stats (path, fn) {fs.stat(path, function (err, stats) {if (err)fn(err, null);fn(null, stats);});
}function reads (filePath,fn){fs.readFile(filePath,function(err,content){if (err)fn(err, null);fn(null, content);});
}function writes(data,fn){fs.writeFile(filePath,data,function(err,content){if (err)fn(err, null);fn(null, content);});
}

var fs = require('fs');
var async = require('async');var path = './async.txt';
async.waterfall([// check if async.txt existsfunction(cb) {fs.stat(path, function(err, stats) {if (stats == undefined) cb(null);else console.log('async.txt exists');});},// read the contents of this filefunction(cb) {fs.readFile(__filename, function(err, content) {var code = content.toString();cb(null, code);});},// write the content to async.txtfunction(code, cb) {fs.writeFile(path, code, function(err) {if (err) throw err;console.log('async.txt created!');});}
]);