callbacksarehard.js

// before
mainWindow.menu("File", function(err, file) {
 if(err) throw err;
 file.openMenu(function(err, menu) {
   if(err) throw err;
   menu.item("Open", function(err, item) {
     if(err) throw err;
     item.click(function(err) {
       if(err) throw err;
       mainWindow.getChild(type('Window'), function(err, dialog) {
         if(err) throw err;
         ...
       });
     });
   });
 });
});

// using named functions
function doSomething (cb) {
  mainWindow.menu("File", onFile)
  function onFile (er, file) {
    if (er) return cb(er)
    file.openMenu(onMenu)
  }
  function onMenu (er, menu) {
    if (er) return cb(er)
    menu.item("Open", onOpen)
  }
  function onOpen (er, item) {
    if (er) return cb(er)
    item.click(onClick)
  }
  function onClick (er) {
    if (er) return cb(er)
    mainWindow.getChild(type("Window"), onGetWindow)
  }
  function onGetWindow (er, dialog) {
    if (er) return cb(er)
    // i presume this is where it ends?
    dialog.doSomething(cb)
  }
}

// this looks like:
// a(cb) --> b(results, cb) --> c(results, cb) ...
// Just a first-pass off-the-cuff flow control abstraction.
// You can do much better than this!
function passAlong () {
  var cb = Array.prototype.pop.call(arguments)
    , steps = Array.prototype.slice.call(arguments)
  n()
  function n (er) {
    if (er) return cb(er)
    var next = steps.shift()
    if (!next) cb.apply(null, arguments)
    else next.apply(null, Array.prototype.slice.call(arguments).concat(n))
  }
}

function doSomething (cb) {
  passAlong
    (function (cb)         { mainWindow.menu("file", cb)             }
    ,function (file, cb)   { file.openMenu(cb)                       }
    ,function (menu, cb)   { menu.item("Open", cb)                   }
    ,function (item, cb)   { item.click(cb)                          }
    ,function (cb)         { mainWindow.getChild(type("Window"), cb) }
    ,function (dialog, cb) { dialog.doSomething(cb)                  }
    ,cb)
}