Simple asyncRunner. Used as an example for what async-await might desugar to.

asyncRunner.js

function subRunner(gen) {
  const state = gen.next();
  const thisPromise = Promise.resolve(state.value);

  return state.done ? thisPromise : thisPromise.then(subRunner(gen));
}

function asyncWrapper(genFunc) {
  return function () {
    try {
      return subRunner(genFunc.apply(this, arguments));
    } catch (e) {
      return Promise.reject(e);
    }
  };
}

module.exports = asyncRunner;

The mapping would look like:

var something = async function (x, y, z) {
  const result = await somethingElse(x);
  // ...
};

to

var something = asyncWrapper(function* (x, y, z) {
  const result = yield somethingElse(x);
  // ...
});