SO comment code

app.js

var fs = require('fs');
var prompt = require('prompt');

// Just a stub to test functionality
fs.fakeExists = function(file, callback) {
  callback(true);
}

// Another stub so we're not actually creating files
fs.fakeWriteFile = function(file, data, callback) {
  callback();
}

function startProcess(callback) {
  prompt.get("file", function(err, results) {
    fs.fakeExists(results.file, function(exists) {
      if (exists) askOverwrite(results.file, callback);
      else createFile(results.file, callback);
    });
  });
}

function askOverwrite(file, callback) {
  console.log("File '" + file + "' exists.");
  prompt.get("overwrite", function(err, results) {
    if (err) return callback(err);

    if (results.overwrite == 'yes') createFile(file, callback);
    else abort();
  });
}

function createFile(file, callback) {
  fs.fakeWriteFile(file, "Some data", callback);
}

function abort() {
  console.log("Aborting creation.");
  process.exit(1);
}

startProcess(function() {
  console.log("All done!");
});

output.txt

btilley@mbair ~/src/sandbox/nodeasync node waterfall.js
prompt: file:  test.txt
File 'test.txt' exists.
prompt: overwrite:  no
Aborting creation.

btilley@mbair ~/src/sandbox/nodeasync node waterfall.js                                                                                                                                                     prompt: file:  test.txt
File 'test.txt' exists.
prompt: overwrite:  yes
All done!