Simple example of async/await transform for Dart's dev_compiler (see https://github.com/dart-lang/dev_compiler/issues/221)

async_example.dart

// Run with dart:
// dart async_example.dart
import 'dart:async';
f(g) async {
    try {
      final value = await g();
      return 'Result: ' + (value + 1);
    } catch (e) {
      if (e == 'rethrow me') throw e;
      return 'Caught: ' + e;
    }
  }

printResult(title, g) => f(g).then(
    (v) => print('[$title] Success Result: $v'),
    onError: (e) => print('[$title] Error Result: $e'));

main() {
  printResult('resolved value', () => new Future.value(10));
  printResult('rejected value', () => new Future.error('error1'));
  printResult('caught error', () { throw 'catch me'; });
  printResult('rethrown error', () { throw 'rethrow me'; });
}

async_example.js

// Run with io.js:
// iojs --harmony_arrow_functions async_example.js
"use strict";
if (typeof dart == "undefined") var dart = {};

dart.Await = function(promise, callback) {
	this.promise = promise;
	this.callback = callback;
};

dart.Future = {
  value: v => new Promise((resolve, reject) => resolve(v)),
  error: e => new Promise((resolve, reject) => reject(e))
};

dart.consumeAwaits = function(iterator) {
  try {
    let result = iterator.next();
    if (result.value instanceof dart.Await) {
      let await = result.value;
      var nextPromise = await.promise.then(
          v => await.callback(() => v),
          e => await.callback(() => { throw e }));
      return result.done ? nextPromise : nextPromise.then(() => dart.consumeAwaits(iterator));
    } else {
      if (!result.done) {
        throw new Error('Invalid state: not expecting non-dart.Await values before the iterator is done.');
      }
      return dart.Future.value(result.value);
    }
  } catch (e) {
    return dart.Future.error(e);
  }
};

var f = (g) => dart.consumeAwaits((function*() {
  var callback$1;
  try {
    var value = ((yield new dart.Await(g(), cb => callback$1 = cb)) || callback$1());
    return 'Result: ' + (value + 1);
  } catch (e) {
    if (e == 'rethrow me') throw e;
    return 'Caught: ' + e;
  }
})());

var printResult = (title, g) => f(g).then(
    v => console.log(`[${title}] Success Result: ${v}`),
    e => console.log(`[${title}] Error Result: ${e}`));

printResult('resolved value', () => dart.Future.value(10));
printResult('rejected value', () => dart.Future.error('error1'));
printResult('caught error', () => { throw 'catch me' });
printResult('rethrown error', () => { throw 'rethrow me' });