nodejs read/write file

fs.readFile('c:\\tmp\\helloworld.txt','utf8',function(err,data){console.log(data);})

var token=fs.readFileSync('c:\\tmp\\toekn.txt','utf8');

fs.writeFile('c:\\tmp\\helloworld.txt', 'Hello World! now, hello again!')

fs.exists('c:\\tmp\\helloworld.txt',function(exists){console.log(exists);})

fs.existsSync('c:\\tmp\\helloworld.txt')