gistfile1.js

var dostuffEmitter = new EventEmitter();

dostuffEmitter.on('task1', function (callback) {
  dostuffEmitter.emit('task2', x, callback);
});

dostuffEmitter.on('task2', function (x, callback) {
  dostuffEmitter.emit('task3', y, callback);
});

dostuffEmitter.on('task3', function (y, callback) {
  dostuffEmitter.emit('finish', z, callback);
});

dostuffEmitter.on('finish', function (z, callback) {
  if (z < 0) {
    callback(0);
  } else {
    callback(z);
  }
});