ES7 Async to ES6 via Babel

1 - script.js

// $ cat script.js

async function foo() {
  res = await fetch("https://example.com");
  return res.ok;
}

2 - script.js

// $ babel -l asyncToGenerator script.js

let foo = _asyncToGenerator(function* () {
  res = yield fetch("https://example.com");
  return res.ok;
});

// Plus a definition for _asyncToGenerator(fn), found below

3 - asyncToGenerator.js

function _asyncToGenerator(fn) {
  return function() {
    var gen = fn.apply(this, arguments);
    return new Promise(function(resolve, reject) {
      var callNext = step.bind(null, "next");
      var callThrow = step.bind(null, "throw");

      function step(key, arg) {
        try {
          var info = gen[key](arg);
          var value = info.value;
        } catch (error) {
          reject(error);
          return;
        }
        
        if (info.done) {
          resolve(value);
        } else {
          Promise.resolve(value).then(callNext, callThrow);
        }
      }
      
      callNext();
    });
  };
}