Completing the initial task before moving on to the next task: Leveraging Ionic 2 Promises

Question

Completing the initial task before moving on to the next task: Leveraging Ionic 2 Promises

Currently in my Ionic 2 project, I am facing an issue where two functions are executing one after another but the second function starts before the first one is completed. Both functions involve making API calls and I want to ensure that the first function finishes its execution entirely before moving on to the second function.

To address this issue, I have been advised to use Promises. I have simplified the code for better readability:

const first = () => {
  self.pspService.post('/api/Conversation/GetPersonalCalendarData',
    {
    }, result => {
      result.Data.forEach(lAppointment => {
        // logic here
      });
    });

  return new Promise((resolve, reject) => {
    resolve();
  });

};

const second = () => {
  self.pspService.post('/api/Conversation/AddPersonalAppointment', {
  }, result => {
    // logic here
  });

  return new Promise((resolve, reject) => {
    resolve();
  });
};

first().then(() => {
  return second();
});

angular typescript ionic-framework ionic2

Answer 1

Answer №1

If you want to encapsulate your post within a new Promise, here is how you can do it:

const initiate = () => {
    return new Promise((resolve, reject) => {
        self.pspService.post('/api/Conversation/GetPersonalCalendarData', {
            }, result => {
                result.Data.forEach(lAppointment => {});
                resolve();
            });
    });

};

const execute = () => {
return new Promise((resolve, reject) => {
    self.pspService.post('/api/Conversation/AddPersonalAppointment', {
        }, result => {
            resolve();
        });
});
};

initiate().then(() => {
     return execute();
});

Alternatively, you could also directly return the promise created by the POST request:

const initiate = () => {
    return self.pspService.post('url, {}, result => {
            result.Data.forEach(lAppointment => {});
            return Promise.resolve(result);
        })
}

Answer 2

If you want to encapsulate your post within a new Promise, here is how you can do it:

const initiate = () => {
    return new Promise((resolve, reject) => {
        self.pspService.post('/api/Conversation/GetPersonalCalendarData', {
            }, result => {
                result.Data.forEach(lAppointment => {});
                resolve();
            });
    });

};

const execute = () => {
return new Promise((resolve, reject) => {
    self.pspService.post('/api/Conversation/AddPersonalAppointment', {
        }, result => {
            resolve();
        });
});
};

initiate().then(() => {
     return execute();
});

Alternatively, you could also directly return the promise created by the POST request:

const initiate = () => {
    return self.pspService.post('url, {}, result => {
            result.Data.forEach(lAppointment => {});
            return Promise.resolve(result);
        })
}

Answer 3

Answer №2

Utilize the updated HttpClient along with switchMap in order to retrieve a distinct Observable

fetchData(){
    return self.dataService.fetchData('/api/Conversation/RetrieveUserData')
          .switchMap((result:any)=>{
            //once you have the "result", you can modify the data
            return self.dataService.post('/api/Conversation/AddUserAppointment')
           });
}
//Within your component
myService.fetchData().subscribe((appointmentData)=>{
    //appointmentData represents the result of self.dataService.post
}

Answer 4

Utilize the updated HttpClient along with switchMap in order to retrieve a distinct Observable

fetchData(){
    return self.dataService.fetchData('/api/Conversation/RetrieveUserData')
          .switchMap((result:any)=>{
            //once you have the "result", you can modify the data
            return self.dataService.post('/api/Conversation/AddUserAppointment')
           });
}
//Within your component
myService.fetchData().subscribe((appointmentData)=>{
    //appointmentData represents the result of self.dataService.post
}

Answer 5

Answer №3

If you encounter situations like this, remember that async/await can be used to manage them effectively. Asynchronous functions are identified by the async keyword; await halts the execution until a promise from an asynchronous function is fulfilled and extracts the value from the returned Promise.

async func(){
    const first = () => {
      self.pspService.post('/api/Conversation/GetPersonalCalendarData',
        {
        }, result => {
          result.Data.forEach(lAppointment => {
          });
        });

      return new Promise((resolve, reject) => {
        resolve();
      });

    };

    const second = () => {
      self.pspService.post('/api/Conversation/AddPersonalAppointment', {
      }, result => {

      });

      return new Promise((resolve, reject) => {
        resolve();
      });
    };

    let firstValue = await first();
    console.log("First Value", firstValue);
    let secondValue = await second();
    console.log("Second Value", secondValue);
  }

Answer 6

If you encounter situations like this, remember that async/await can be used to manage them effectively. Asynchronous functions are identified by the async keyword; await halts the execution until a promise from an asynchronous function is fulfilled and extracts the value from the returned Promise.

async func(){
    const first = () => {
      self.pspService.post('/api/Conversation/GetPersonalCalendarData',
        {
        }, result => {
          result.Data.forEach(lAppointment => {
          });
        });

      return new Promise((resolve, reject) => {
        resolve();
      });

    };

    const second = () => {
      self.pspService.post('/api/Conversation/AddPersonalAppointment', {
      }, result => {

      });

      return new Promise((resolve, reject) => {
        resolve();
      });
    };

    let firstValue = await first();
    console.log("First Value", firstValue);
    let secondValue = await second();
    console.log("Second Value", secondValue);
  }

Completing the initial task before moving on to the next task: Leveraging Ionic 2 Promises

Answer №1

Answer №2

Answer №3

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