async-to-generator.js

function __async (generator) {
  return function (...args) {
    let it = generator.apply(this, args);

    return new Promise((resolve, reject) => {
      step(it.next());
      
      function step (result) {
        if (result.done) resolve(result.value);
        else Promise.resolve(result.value).then(fulfilled, rejected);
      }

      function fulfilled (value) {
        try {
          step(it.next(value));
        } catch (e) {
          reject(e);
        }
      }

      function rejected (value) {
        try {
          step(it.throw(value));
        } catch (e) {
          reject(e);
        }
      }
    });
  }
}