coroutine.js

// coroutine for callback
function coroutineC(gen, handler) {
  let cb = function (err, value) {
    switch (err) {
      case undefined:
      case null:
        process.nextTick(function () {
          try {
            g.next(value)
          } catch (ex) {
            cb(ex);
          }
        });
        break;
      default:
        if (typeof handler === 'function') handler(err);
        else throw err;
    }
  };
  let g = gen(cb);
  cb();
}

// coroutine for promise
function coroutineP(gen) {
  return new Promise(function (resolve, reject) {
    const g = gen();
    const reply = function (res) {
      let x;
      try {
        // x.value :: Promise
        x = g.next(res);
      } catch (ex) {
        reject(ex);
        return;
      }

      if (x.done) resolve(x.value);
      else x.value.then(reply).catch(reject);
    };
    reply();
  })
}

module.exports = { coroutineC, coroutineP };