Using AJAX to retrieve JSON information

Question

Using AJAX to retrieve JSON information

Looking for advice on improving my script to fetch JSON data from a server file using AJAX. I am struggling with organizing it into a functional structure.

Below is the current implementation:

function getJSON (file) {
    var request = AjaxRequest();
    var json = "";
    request.onreadystatechange = function () {
        if(request.readyState == 4 && request.status == 200) {
            json = JSON.parse(request.responseText);
        }
    }
    request.open("GET", file, false);
    request.send();
    return json;
}

Although the function meets my requirements, I have received feedback advising against passing 'false' as an argument in the AJAX request due to potential blocking issues. This leaves me unsure about the correctness of my approach. Any suggestions on how I can improve this function? Should I make any changes, and if so, what modifications would be appropriate?

javascript ajax json

Answer 1

Answer №1

The return process cannot happen immediately in this case because it is an asynchronous operation. Your

json = JSON.parse(request.responseText)

will only occur later once the server responds with data, which may be long after the return statement has already executed. To address this, you can modify your function to accept a callback that handles the returned data:

function getJSON (file, callback)
{
  var request = AjaxRequest();
  request.onreadystatechange = function ()
  {
     if(request.readyState==4 && request.status==200)
     {
       callback(JSON.parse(request.responseText));
     }
  }
  request.open("GET", file, false);
  request.send();
}

To implement this change, you would call the function like so:

getJSON("something.json", function(data) { 
  //utilize the received data, your json object/data
});

In this manner, you are effectively utilizing the data as soon as it becomes available and passing it along to subsequent functions, aligning with the intended behavior of asynchronous calls.

Answer 2

The return process cannot happen immediately in this case because it is an asynchronous operation. Your

json = JSON.parse(request.responseText)

will only occur later once the server responds with data, which may be long after the return statement has already executed. To address this, you can modify your function to accept a callback that handles the returned data:

function getJSON (file, callback)
{
  var request = AjaxRequest();
  request.onreadystatechange = function ()
  {
     if(request.readyState==4 && request.status==200)
     {
       callback(JSON.parse(request.responseText));
     }
  }
  request.open("GET", file, false);
  request.send();
}

To implement this change, you would call the function like so:

getJSON("something.json", function(data) { 
  //utilize the received data, your json object/data
});

In this manner, you are effectively utilizing the data as soon as it becomes available and passing it along to subsequent functions, aligning with the intended behavior of asynchronous calls.

Using AJAX to retrieve JSON information

Answer №1

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