var api1 = 'https://anapioficeandfire.com/api/characters/583'var api2 = 'https://anapioficeandfire.com/api/characters/584'function *fetchData () {  var res = yield request(api1)  res.json().then(data => {    console.log(data.name) // Jon Snow  })}function request (url) {  fetch(url).then(res => {    it.next(res)  })}var it = fetchData()it.next()var api1 = 'https://anapioficeandfire.com/api/characters/583'var api2 = 'https://anapioficeandfire.com/api/characters/584'function *fetchData () {  var res = yield fetch(api1).then(data => fetchData().next(data))  res.json().then(data => {    console.log(data.name)  })}fetchData().next()第一段代碼可以正確打印出結果，而第二段代碼卻不行，想問下為什么，我覺得兩段代碼并沒有區別