generator, promise.

co.js

function co (_g) {
  const ge = _g()
  next(ge)
}

function next(ge, _v) {
  const { value, done } = ge.next(_v)
  if (done) {
    ge.next(value)
  } else {
    if (typeof value.then === 'function') {
      value.then(result => {
        next(ge, result)
      }).catch(e => {
      	ge.throw(e)
      })
    } else {
      next(ge, value)
    }
  }
}

co(function *() {
  try {
    const a = yield Promise.resolve(1)
    const b = 2
    console.log(a, b)
    const c = yield Promise.reject(3)
    console.log(a + b + c)
  } catch (e) {
    console.log('catchchchc')
  } 
})