Avoiding Nested Callbacks in Javascript

example1.js

var fs = require('fs');

fs.mkdir('./hello',0777,makeDirectory);

function makeDirectory(err){
  if (err) throw err;
  fs.writeFile('./hello/world.txt', 'Hello!', writeFile);
}

function writeFile(err){
  if (err) throw err;
  console.log('File created with contents: ');
  fs.readFile('./hello/world.txt', 'UTF-8', readFile);
}

function readFile(err, data){
  if (err) throw err;
  console.log(data);
}

example2.js

var fs = require('fs');

function writeHello(){
  return fs.writeFile('./hello.txt', 'Hello!', writeFile);

  function writeFile(err){
    if (err) throw err;
    console.log('Wrote hello.txt');
  }
}

function writeWorld(){
  return fs.writeFile('./world.txt', 'World!', writeFile);

  function writeFile(err){
    if (err) throw err;
    console.log('Wrote world.txt');
  }
}

writeHello();
writeWorld(); 

nested.js

var fs = require('fs');

fs.mkdir('./hello',0777,function(err){
  if (err) throw err;

  fs.writeFile('./hello/world.txt', 'Hello!', function(err){
    if (err) throw err;
    console.log('File created with contents: ');

    fs.readFile('./hello/world.txt', 'UTF-8', function(err, data){
      if (err) throw err;
      console.log(data);
    });
  });
});