異步等待未按預期回傳值

我對 Async Await 有基本的了解，但我似乎遺漏了一些東西。

請參閱下面的代碼。我已經放置了 console.log 行來跟蹤執行。我希望每個 console.log 都應該按順序回傳令牌。但“Token1”和“Token3”回傳“未定義”，而“Token2”回傳實際令牌。

問題：

• 我是否正確使用異步等待？
• 我是否正確回傳“credentials.access_token”？

async function GetAuthTokenAsync() {
  // Initialize the 2-legged OAuth2 client, set specific scopes and optionally set the `autoRefresh` parameter to true
  // if you want the token to auto refresh
  var autoRefresh = true; // or false

  var oAuth2TwoLegged = new ForgeSDK.AuthClientTwoLegged(
    FORGE_CLIENT_ID,
    FORGE_CLIENT_SECRET,
    ["data:read", "data:write"],
    autoRefresh
  );

  oAuth2TwoLegged.authenticate().then(
    function (credentials) {
      // The `credentials` object contains an access_token that is being used to call the endpoints.
      // In addition, this object is applied globally on the oAuth2TwoLegged client that you should use when calling secure endpoints.
      console.log("Token2: ", credentials.access_token);                 //RETURNS THE TOKEN
      return credentials.access_token;
      },
    function (err) {
      console.error(err);
    }
  );
}

async function Token() {
  const token = await GetAuthTokenAsync();
  console.log("Token1: ", token);                                        //RETURNS 'undefined'
  return token;
}

Token().then(AuthToken => console.log('Token3: ', AuthToken));           //RETURNS 'undefined'

uj5u.com熱心網友回復：

你沒有正確使用它。每個異步函式都回傳一個Promise，但如果你沒有明確的 return 陳述句，它將回傳一個已決議的 promise，其值為undefined. 這就是為什么您將 Token1 視為undefined. 您GetAuthTokenAsync運行呼叫，但它沒有await結果并且不回傳任何內容。

我已經標記了您的代碼，以顯示下面需要進行哪些更改。

async function GetAuthTokenAsync() {
  // Initialize the 2-legged OAuth2 client, set specific scopes and optionally set the `autoRefresh` parameter to true
  // if you want the token to auto refresh
  var autoRefresh = true; // or false

  var oAuth2TwoLegged = new ForgeSDK.AuthClientTwoLegged(
    FORGE_CLIENT_ID,
    FORGE_CLIENT_SECRET,
    ["data:read", "data:write"],
    autoRefresh
  );

  return oAuth2TwoLegged.authenticate().then(   // <---- Must return a promise
    function (credentials) {
      // The `credentials` object contains an access_token that is being used to call the endpoints.
      // In addition, this object is applied globally on the oAuth2TwoLegged client that you should use when calling secure endpoints.
      console.log("Token2: ", credentials.access_token);                 //RETURNS THE TOKEN
      return credentials.access_token;
      },
    function (err) {
      console.error(err);
    }
  );
}

async function Token() {
  const token = await GetAuthTokenAsync();
  console.log("Token1: ", token);                                        //RETURNS 'undefined'
  return token;
}

Token().then(AuthToken => console.log('Token3: ', AuthToken));

此外，允許在函式.then內部使用async，但它會使其更難閱讀。可以這樣簡化：

async function GetAuthTokenAsync() {
  // Initialize the 2-legged OAuth2 client, set specific scopes and optionally set the `autoRefresh` parameter to true
  // if you want the token to auto refresh
  var autoRefresh = true; // or false

  var oAuth2TwoLegged = new ForgeSDK.AuthClientTwoLegged(
    FORGE_CLIENT_ID,
    FORGE_CLIENT_SECRET,
    ["data:read", "data:write"],
    autoRefresh
  );

  const credentials = await oAuth2TwoLegged.authenticate();
  console.log("Token2: ", credentials.access_token);                 
  //RETURNS THE TOKEN
  return credentials.access_token;
}

如果您真的想捕獲并 console.log 里面的錯誤，GetAuthTokenAsync那么您可以添加一個.catch()函式，但最好讓錯誤通常被拋出堆疊。

uj5u.com熱心網友回復：

你必須這樣做

async function GetAuthTokenAsync() {
    // Initialize the 2-legged OAuth2 client, set specific scopes and optionally set the `autoRefresh` parameter to true
    // if you want the token to auto refresh
    var autoRefresh = true; // or false
  
    var oAuth2TwoLegged = new ForgeSDK.AuthClientTwoLegged(
      FORGE_CLIENT_ID,
      FORGE_CLIENT_SECRET,
      ["data:read", "data:write"],
      autoRefresh
    );
  
    // you need to await the token before you can use it
    const credentials = await oAuth2TwoLegged.authenticate()
    // .then(
    //   function (credentials) {
    //     // The `credentials` object contains an access_token that is being used to call the endpoints.
    //     // In addition, this object is applied globally on the oAuth2TwoLegged client that you should use when calling secure endpoints.
    //     console.log("Token2: ", credentials.access_token);                 //RETURNS THE TOKEN
    //     return credentials.access_token;
    //     },
    //   function (err) {
    //     console.error(err);
    //   }
    // );

    return credentials.access_token;
  }
  
  async function Token() {
    const token = await GetAuthTokenAsync();
    console.log("Token1: ", token);                                        //RETURNS 'undefined'
    return token;
  }
  
  Token().then(AuthToken => console.log('Token3: ', AuthToken)); 

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