如何在回呼函式中取消待處理的承諾呼叫？

fetch(
  "https://rqyhfmwv4b.execute-api.us-east-1.amazonaws.com/production/join-meeting",
  requestOptions
).then((response) => response.json())
.then(async (data) => {
  // You need responses from server-side Chime API. See below for details.
  const meetingResponse =
  data.result
  .meetingResponsee; /* The response from the CreateMeeting API action */
  const attendeeResponse =
  data.result
  .attendeeResponsee; /* The response from the CreateAttendee or BatchCreateAttendee API action */
  const configuration = new MeetingSessionConfiguration(
    meetingResponse,
    attendeeResponse
  );
  
  // In the usage examples below, you will use this meetingSession object.
  const meetingSession = new DefaultMeetingSession(
    configuration,
    logger,
    deviceController
  );
  
  const meetingReadinessChecker = new DefaultMeetingReadinessChecker(
    logger,
    meetingSession
  );
  
  // testing
  
  if (pauseReadinessTest) {
    setPauseReadinessTest(false);
    return;
  }
  
  if (testParam == "All" && disableStartRedinessTest !== true) {
    await audioTest(deviceController);
    setMeetingTestProgress(15);
    await micTest(meetingSession, meetingReadinessChecker, CheckAudioInputFeedback);
    setMeetingTestProgress(25);
    await videoTest(meetingSession, meetingReadinessChecker, CheckVideoInputFeedback);
    await cameraTest(meetingSession, meetingReadinessChecker, CheckCameraResolutionFeedback);
    setMeetingTestProgress(50);
    await networkTest(meetingReadinessChecker, CheckNetworkTCPConnectivityFeedback, CheckNetworkUDPConnectivityFeedback);
    setMeetingTestProgress(75);
    await streamTest(meetingSession, meetingReadinessChecker, CheckAudioConnectivityFeedback, CheckVideoConnectivityFeedback);
    setMeetingTestProgress(85);
    await screenShareTest(meetingSession, meetingReadinessChecker, CheckContentShareConnectivityFeedback);
    setMeetingTestProgress(100);
    setRefreshIconClass(" ");
    SetDisableStartRedinessTest(false);
    setIsResult("result");
}

我有這段代碼，如果用戶想要退出測驗，我想取消掛起的等待函式呼叫。但問題是，每當變數的值被更新時，它都不會反映在導致主要問題的塊內。

uj5u.com熱心網友回復：

據我所知，promise 概念主要是一種語法糖。現實世界中會發生什么 - 您在函式呼叫 (A) 中傳遞一個回呼函式 (B)，并且在某個時刻函式 A 將呼叫函式 B。如果您在撰寫函式 A 時沒有考慮到取消概念，則有沒有辦法取消通話。更容易使用其他方法（全域變數、額外傳遞的物件引數等）來設定標志“不運行”并在函式 B 中檢查它。

uj5u.com熱心網友回復：

你可以這樣做：

const promises = [{
    functionCall: () => audioTest(deviceController), 
    progress: 15,
}, {
    functionCall: await micTest(meetingSession, meetingReadinessChecker, CheckAudioInputFeedback),
    progress: 25,
    }, // ...etc.
];

while (testParam == "All" && disableStartRedinessTest !== true && promises.length) {
    const { functionCall, progress } = promises.unshift();
    await functionCall.call(this);
    setMeetingTestProgress(progress);
}

雖然如果你正在考慮取消操作，我會使用 RxJS 而不是 vanilla Promise。

uj5u.com熱心網友回復：

如果您在回呼函式中有待處理的承諾，您可以使用 Promise.prototype.cancel() 方法取消它。例如：

var promise = new Promise(function(resolve, reject) {
  // do something

  if (/* some condition */) {
    resolve(); // or reject(), depending on your needs
  } else {
    promise.cancel(); // this will cancel the pending promise and prevent it from being resolved or rejected
  }
});

標籤：javascript 反应 异步 异步等待 承诺

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