Javascript：编写返回承诺的函数

我试图在Firebase函数中创建一个函数，该函数返回一个承诺（或者同步返回，我不介意），但没有成功

以下是我编写的函数：

function doSomethingLong(param) {
    https.get('http://www.myurl.com?param=' + param, (resp) => {
        let data = '';

        // A chunk of data has been recieved.
        resp.on('data', (chunk) => {
            data += chunk;
        });

        // The whole response has been received. Print out the result.
        resp.on('end', () => {
            console.log("Call succeeded. Response: " + data);
            return true;
        });
    }).on("error", (err) => {
        console.log("Call failed. Error: " + err.message);
        return false;
    });
}

我想在Firebase发生某种变化时调用它，并等待它完成，比如：

exports.someFunction = functions.database.ref('/users/{user_id}/param').onCreate(event => {
    const param = event.data.val();

    if (doSomethingLong(param)) {
        console.log("ttt");
    } else {
        console.log("fff");
    }
    return null;
})

不管我怎么做，

someFunction

函数在

doSomethingLong

结束之前结束

---

有什么线索吗？

异步任务结束时，您必须创建一个承诺并解决/拒绝它

function doSomethingLong(param) {

   return new Promise(function(resolve, reject){

       https.get('http://www.myurl.com?param=' + param, (resp) => {
          let data = '';

          // A chunk of data has been recieved.
          resp.on('data', (chunk) => {
              data += chunk;
          });

          // The whole response has been received. Print out the result.
          resp.on('end', () => {
              console.log("Call succeeded. Response: " + data);
              resolve();
          });
      }).on("error", (err) => {
          console.log("Call failed. Error: " + err.message);
          reject(err);
      });
   });
}

现在你可以这样使用它了

doSomethingLong()
   .then(function() {
      console.log(pased)
   },

   function(err) {
     console.log(err)
   }

)

---

您必须创建一个承诺，并在异步任务结束时解决/拒绝它

function doSomethingLong(param) {

   return new Promise(function(resolve, reject){

       https.get('http://www.myurl.com?param=' + param, (resp) => {
          let data = '';

          // A chunk of data has been recieved.
          resp.on('data', (chunk) => {
              data += chunk;
          });

          // The whole response has been received. Print out the result.
          resp.on('end', () => {
              console.log("Call succeeded. Response: " + data);
              resolve();
          });
      }).on("error", (err) => {
          console.log("Call failed. Error: " + err.message);
          reject(err);
      });
   });
}

现在你可以这样使用它了

doSomethingLong()
   .then(function() {
      console.log(pased)
   },

   function(err) {
     console.log(err)
   }

)

像这样做

    function doSomethingLong(param) {
    return new Promise(function(resolve,reject){
        https.get('http://www.myurl.com?param=' + param, (resp) => {
            let data = '';

            // A chunk of data has been recieved.
            resp.on('data', (chunk) => {
                data += chunk;
            });

            // The whole response has been received. Print out the result.
            resp.on('end', () => {
                console.log("Call succeeded. Response: " + data);
                resolve(data);//resolve data
            });
        }).on("error", (err) => {
            console.log("Call failed. Error: " + err.message);
            reject(err);//reject(reason)
        });
    });
}


exports.someFunction = functions.database.ref('/users/{user_id}/param').onCreate(event => {
    const param = event.data.val();

    if (addUserToNewsletter(user_id, name, email, language)) {
        console.log("ttt");
    } else {
        console.log("fff");
    }
    return null;
    let promise=doSomethingLong('foo');
    promise.then((data)=>{
        console.log(data);
    }).catch((err)=>{
        console.log(err);
    })
})

像这样做

    function doSomethingLong(param) {
    return new Promise(function(resolve,reject){
        https.get('http://www.myurl.com?param=' + param, (resp) => {
            let data = '';

            // A chunk of data has been recieved.
            resp.on('data', (chunk) => {
                data += chunk;
            });

            // The whole response has been received. Print out the result.
            resp.on('end', () => {
                console.log("Call succeeded. Response: " + data);
                resolve(data);//resolve data
            });
        }).on("error", (err) => {
            console.log("Call failed. Error: " + err.message);
            reject(err);//reject(reason)
        });
    });
}


exports.someFunction = functions.database.ref('/users/{user_id}/param').onCreate(event => {
    const param = event.data.val();

    if (addUserToNewsletter(user_id, name, email, language)) {
        console.log("ttt");
    } else {
        console.log("fff");
    }
    return null;
    let promise=doSomethingLong('foo');
    promise.then((data)=>{
        console.log(data);
    }).catch((err)=>{
        console.log(err);
    })
})

---

你可以通过返回一个承诺、承诺、决心或承诺、拒绝，将两者结合起来

使您的代码看起来像这样：

 this.props.doSomethingLong(loginResult.credential)
          .then(result => this.someFunction(result))
          .catch(error => this.handleError(error.message))

这样做：

exports.someFunction = functions.database.ref('/users/{user_id}/param').onCreate(event => {
const param = event.data.val();

if (addUserToNewsletter(user_id, name, email, language)) {
    console.log("ttt");
} else {
    console.log("fff");
}
return Promise.resolve();

})

---

在每次函数调用中执行此操作，您可以在中阅读更多有关承诺及其工作方式的信息。您可以通过返回承诺、承诺.resolve或承诺.reject将它们连接起来

使您的代码看起来像这样：

 this.props.doSomethingLong(loginResult.credential)
          .then(result => this.someFunction(result))
          .catch(error => this.handleError(error.message))

这样做：

exports.someFunction = functions.database.ref('/users/{user_id}/param').onCreate(event => {
const param = event.data.val();

if (addUserToNewsletter(user_id, name, email, language)) {
    console.log("ttt");
} else {
    console.log("fff");
}
return Promise.resolve();

})

---

在每次函数调用中执行此操作，您可以阅读更多关于承诺及其如何在

中工作的信息，因此，您需要运行doSomethingLong，然后在resp.on（'end'）触发后，将结果“data”传递给某个函数，对吗？如果我没有弄错的话，这就是您试图实现的目标：（修复了原始问题中的一些误导性输入错误）@KostasX，我试图实现的是：当调用someFunction时，它应该调用doSomethingLong，等待它完成，然后才返回。因此，可能的重复是，您想要运行doSomethingLong，然后在resp.on（'end'）激发后，将结果“data”传递给someFunction，对吗？如果我没有弄错的话，这就是你想要达到的目标：（修正了原问题中一些误导性的拼写错误）@KostasX，我试图实现的是：当调用某个函数时，它应该调用doSomethingLong，等待它完成，然后才返回