wasn't able to write the buffer stream into a newly created directory in nodeJs

I had to create a directory named stuff and write the stream into a text file inside the "stuff" directory. but, because the code in NodeJs doesn't execute in a serial fashion, I m getting an error which says the directory doesn't exist. any help would be appreciated. the code is pasted below.

var http = require("http");

var fs = require("fs");

var readStream = fs.createReadStream(__dirname+"/readMe.txt","UTF-8");

  var writeStream;

  fs.mkdir("stuff",function(){

     writeStream = fs.createWriteStream(__dirname+"/stuff/writeMe.txt");

 });

readStream.on("data",function(chunk){

writeStream.write(chunk);

});

via The-Higgs-Boson