generator executor

calling-code.js

const context = {
  sayHello: (message) => console.log(`hello, world! ${message}`)
};

function *doSomething() {
  yield 1;
  yield 2;
  this.sayHello('about to yield!');
  const three = yield new Promise((resolve, reject) => {
    setTimeout(() => resolve(3), 1000);
  });
  this.sayHello(`done yielding!, got ${three}`);
}

executeGenerator(doSomething, context)
  .then(() => console.log('done!'));

executeGenerator.js

function executeGenerator(generator, context) {
  return new Promise(function (resolve, reject) {
    var iterator = generator.call(context);

    var current;

    function iterate(val) {
      current = iterator.next(val);
      if (current.done) {
        resolve(current.value);
      } else {
        if (current.value && 'then' in current.value) {
          current.value.then(iterate);
        } else {
          setImmediate(() => {
            iterate(current.value);
          });
        }
      }
    }

    iterate();
  });
}