异步等待未按预期返回值

Question

我对异步等待有了基本的理解，但我似乎遗漏了一些东西。

请参阅下面的代码。我在整个过程中放置了console.log行来跟踪执行。我希望每个console.log都应该按照顺序返回令牌。但是'Token1‘和'Token3’返回‘未定义’，而'Token2‘返回实际的令牌。

问题：

• 我正在正确地使用异步等待吗？
• 我返回了credentials.access_token正确吗？

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'

Answer 1

你没有很好地使用它。每个异步函数都返回一个Promise，但是如果没有显式返回语句，它将返回一个值为undefined的解析承诺。这就是为什么您将Token1视为undefined的原因。您的GetAuthTokenAsync运行该调用，但它不对结果进行await，也不返回任何内容。

我已经标记了您的代码，以显示需要在下面进行哪些更改。

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，允许在.then函数中使用async，但这会增加读取难度。它可以简化如下：

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;
}

如果您真的想捕获& console.log，GetAuthTokenAsync内部的错误，那么您可以添加一个.catch()函数，但是最好通常让错误抛出堆栈。

Answer 2

你必须这样做

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));