ジェネレータの解説と非同期への適用 完成品 http://jxck.hatenablog.com/entry/2014-01-12/generator-screencaset

a.txt

b.txt

b.txt

c.txt

c.txt

goal!

file.js

var fs = require('fs');

co(function* generator() {
  var read = thunkify(fs.readFile);
  try {
    var path = 'a.txt';
    var b = yield read(path, 'utf8');
    b = b.replace('\n', '');

    var c = yield read(b, 'utf8');
    c = c.replace('\n', '');

    var result = yield read(c, 'utf8');
    result = result.replace('\n', '');

    console.log(result);
  } catch (err) {
    console.error(err);
  }
})();

///////////////////////////////////////////////////////

function co(generator) {
  var g = generator();

  function done(err, data) {
    if (err) {
      return g.throw(err);
    }
    var n = g.next(data);
    if (n.done) {
      return;
    }
    n.value(done);
  }

  return function() {
    g.next().value(done);
  }
}

function thunkify(fn) {
  return function() {
    var args = Array.prototype.slice.call(arguments);
    return function(callback) {
      args.push(callback);
      fn.apply(this, args);
    }
  }
}

generator.js

function* generator() {
  var a = yield(function() { console.log('x'); return 1 })();
  console.log(a);

  var b = yield(function() { console.log('y'); return 2 })();
  console.log(b);

  var c = yield(function() { console.log('z'); return 3 })();
  console.log(c);

  return 4;
}

var g = generator();
console.log(g.next());
console.log(g.next(10));
console.log(g.next(20));
console.log(g.next(30));