The axios GET request failed to return a defined value

Question

The axios GET request failed to return a defined value

My current issue involves making a get request using the following code snippet:

router.get('/marketUpdates',((request, response) => {
  console.log("market updates");
  var data: Order[]
  axios.get('http://localhost:8082/marketUpdates')
  .then(function (response) {
    console.log("GET Response")
    console.log(response.data);
    data = response.data;
  })
  .catch(function (error) {
    console.log("Error in fetching market updates");
  });  

  console.log("Data before sending is ")
  console.log(data);
  response.send(data);
}))

However, I am facing a problem where my final console.log statement at the bottom executes before the console.log within the .then block.

This leads to 'data' being undefined when it gets sent. Does anyone have any suggestions on how to resolve this timing issue?

javascript http typescript asynchronous

Answer 1

Answer №1

When working with asynchronous code, make sure to keep in mind that the execution continues while waiting for a response. To avoid issues, move any logs from below the request above the axios.get call.
Ensure consistency in your data handling by using arrow functions instead of function expressions inside the `then` method. This will prevent inadvertently binding another `this`.

Consider restructuring your code like this:

router.get('/marketUpdates',((request, response) => {
  console.log("market updates");
  let data: Order[]
  console.log("Data before sending is ")
  console.log(data);
  axios.get('http://localhost:8082/marketUpdates')
  .then((getResponse) => {
    console.log("GET Response")
    console.log(getResponse.data);
    data = getResponse.data;
    response.send(data);
  })
  .catch(function (error) {
    console.log("Error while fetching market updates");
  });  
}))

Answer 2

When working with asynchronous code, make sure to keep in mind that the execution continues while waiting for a response. To avoid issues, move any logs from below the request above the axios.get call.
Ensure consistency in your data handling by using arrow functions instead of function expressions inside the `then` method. This will prevent inadvertently binding another `this`.

Consider restructuring your code like this:

router.get('/marketUpdates',((request, response) => {
  console.log("market updates");
  let data: Order[]
  console.log("Data before sending is ")
  console.log(data);
  axios.get('http://localhost:8082/marketUpdates')
  .then((getResponse) => {
    console.log("GET Response")
    console.log(getResponse.data);
    data = getResponse.data;
    response.send(data);
  })
  .catch(function (error) {
    console.log("Error while fetching market updates");
  });  
}))

Answer 3

Answer №2

When requests are sent to a server, they are always asynchronous. This means that the function .then() will only be executed once the server has responded.

Allow me to reformat your code for better clarity:

router.get('/marketUpdates',((request, response) => {
  console.log("market updates");

  var data: Order[];

  console.log("Data before sending is ")
  console.log(data);

  axios.get('http://localhost:8082/marketUpdates')
  .then((response) => {
    console.log("GET Response")
    console.log(response.data);
    data = response.data;

    response.send(data);
  })
  .catch(function (error) {
    console.log("Error in fetching market updates");
  });  
}))

By including the line

axios.get('http://localhost:8082/marketUpdates')

, you are initiating a request to the server. However, this process takes time as the server needs to respond. JavaScript does not pause its execution while waiting for the server response to ensure smooth running of the user interface.

Therefore, the .get method returns a Promise containing various functions that are invoked under specific circumstances. The function provided as the first parameter to .then will be called once the server responds with a status code of 200 and a valid response.

As a result, the logs at the end of your code snippet will be executed immediately after axios sends the request to the server. At this point, there won't be any data available since the server has yet to provide a response.

Answer 4

When requests are sent to a server, they are always asynchronous. This means that the function .then() will only be executed once the server has responded.

Allow me to reformat your code for better clarity:

router.get('/marketUpdates',((request, response) => {
  console.log("market updates");

  var data: Order[];

  console.log("Data before sending is ")
  console.log(data);

  axios.get('http://localhost:8082/marketUpdates')
  .then((response) => {
    console.log("GET Response")
    console.log(response.data);
    data = response.data;

    response.send(data);
  })
  .catch(function (error) {
    console.log("Error in fetching market updates");
  });  
}))

By including the line

axios.get('http://localhost:8082/marketUpdates')

, you are initiating a request to the server. However, this process takes time as the server needs to respond. JavaScript does not pause its execution while waiting for the server response to ensure smooth running of the user interface.

Therefore, the .get method returns a Promise containing various functions that are invoked under specific circumstances. The function provided as the first parameter to .then will be called once the server responds with a status code of 200 and a valid response.

As a result, the logs at the end of your code snippet will be executed immediately after axios sends the request to the server. At this point, there won't be any data available since the server has yet to provide a response.

The axios GET request failed to return a defined value

Answer №1

Answer №2

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