Callbacks

function asyncMethod(message, callback_function) { 
  setTimeOut( function() { 
    console.log(message); 
    callback_function(); 
   }, 400) 
} 

asyncMethod('Connect to Database', function() { 
} 

Nested Callbacks

asyncMethod('Connect to Database', function() { 
  asyncMethod('Verify User Details', function() { 
    asyncMethod('Check Permissions', function() { 
      asyncMethod('Update User', function() {} ) 
    }) 
  }) 
}) 

Best Practices

Arguments should be (err, results)
Always 'return' when you want to exit