Javascript：返回承諾的寫函數

Question

我正在嘗試在Firebase Functions中創建一個返回諾言（或同步返回，我不介意）的函數，但是沒有成功。

這是我編寫的函數：

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發生某些更改時調用它，然后等待它完成，例如：

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;
})

無論我如何嘗試， someFunction函數都會在doSomethingLong結束之前結束。

有什么線索嗎？

Answer 1

您必須創建一個Promise並在異步任務結束時解決/拒絕它。

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);
      });
   });
}

現在您可以像這樣使用它

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

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

)

Answer 2

做類似的事情，

    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);
    })
})

Answer 3

您可以通過返回promise，promise.resolve或promise.reject來使它們同時加入。

使您的代碼看起來像這樣：

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

這樣做：

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();

}）

進行每個函數調用，您都可以了解有關Promises及其在Node-js中的工作方式的更多信息。