Angular 4 yields an undefined result

Question

Angular 4 yields an undefined result

I'm currently working on this piece of code and I need help figuring out how to return the value of rowData in this scenario.

private createRowData() {
const rowData: any[] = [];

this.http
  .get(`/assets/json/payment.json`)
  .toPromise()
  .then(response => response.json())
  .then(data => {
    data.items.map(elem => {
      rowData.push({
        id: elem.id,
        total_amount: elem.total_amount,
        status: elem.status,
        sent: elem.sent,
      });
    });
  });
return rowData;}

Before returning, I attempted to console log rowData but it returned undefined.

angular typescript

Answer 1

Answer №1

Your function must provide a promise that contains the transformed data. In the final then callback, make sure to return the transformed response. Utilize the implicit return of arrow functions for this purpose without needing the variable rowData since array.proptype.map generates a new array with each value transformed. Simply follow these steps:

private fetchTransformedData() {
   return this.http    // Return the promise
    .get(`/assets/json/payment.json`)
    .toPromise()
    .then(response => response.json())
    .then(data => data.items.map(elem => ({   // Return the transformed data by the then callback
        id: elem.id,
        total_amount: elem.total_amount,
        status: elem.status,
        sent: elem.sent,
     })));
}

You can then utilize this function in the following way:

this.fetchTransformedData().then(result => console.log(result))

Answer 2

Your function must provide a promise that contains the transformed data. In the final then callback, make sure to return the transformed response. Utilize the implicit return of arrow functions for this purpose without needing the variable rowData since array.proptype.map generates a new array with each value transformed. Simply follow these steps:

private fetchTransformedData() {
   return this.http    // Return the promise
    .get(`/assets/json/payment.json`)
    .toPromise()
    .then(response => response.json())
    .then(data => data.items.map(elem => ({   // Return the transformed data by the then callback
        id: elem.id,
        total_amount: elem.total_amount,
        status: elem.status,
        sent: elem.sent,
     })));
}

You can then utilize this function in the following way:

this.fetchTransformedData().then(result => console.log(result))

Answer 3

Answer №2

When you make an asynchronous http call, it's crucial to handle the data retrieval properly to avoid getting undefined values. One common mistake is executing the return rowData; line before the call is complete, resulting in an incomplete response. To fix this issue, consider returning a promise from your function and utilizing a .then() call to fetch the rowData object once the operation is finished.

private fetchData() {
  const rowData: any[] = [];

  return this.http  
   .get(`/assets/json/data.json`)
   .toPromise()
   .then(response => response.json())
   .then(data => {
     data.items.map(elem => {
      rowData.push({
        id: elem.id,
        total_amount: elem.total_amount,
        status: elem.status,
        sent: elem.sent
      });
      return rowData;
    });
  });

}

ngOnInit() {
  this.fetchData().then(data => {
    console.log(data) 
  });
}

Answer 4

When you make an asynchronous http call, it's crucial to handle the data retrieval properly to avoid getting undefined values. One common mistake is executing the return rowData; line before the call is complete, resulting in an incomplete response. To fix this issue, consider returning a promise from your function and utilizing a .then() call to fetch the rowData object once the operation is finished.

private fetchData() {
  const rowData: any[] = [];

  return this.http  
   .get(`/assets/json/data.json`)
   .toPromise()
   .then(response => response.json())
   .then(data => {
     data.items.map(elem => {
      rowData.push({
        id: elem.id,
        total_amount: elem.total_amount,
        status: elem.status,
        sent: elem.sent
      });
      return rowData;
    });
  });

}

ngOnInit() {
  this.fetchData().then(data => {
    console.log(data) 
  });
}

Angular 4 yields an undefined result

Answer №1

Answer №2

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