JSON Nested Elements Undefined

Question

I am having extreme difficulty accessing nested values in JSON arrays, and for the life of me cannot figure out why my attempts are resulting in undefined values. I am trying to get the distance between two postcodes using the Google Distance Matrix API.

For full explanation, see the bottom of this post. For now, I will show the code performing the operations.

When the user completes entering the postcode for the origin and the destination, the following JavaScript function is called:

function calculateDistance(){

    var origin = $("#ex_origin").val(); // Success
    var destination = $("#ex_dest").val(); // Success

    obj = { "origin" : origin, "destination" : destination   }; // Set up JSON Object
        dbParam = JSON.stringify(obj); // Convert the object into a string to be used by the PHP file

        xhttp = new XMLHttpRequest();
        xhttp.onreadystatechange = function() {
            if (this.readyState == 4 && this.status == 200) {
                var result = JSON.parse(this.responseText); // Parse the JSON string so it can be read by JavaScrippt
                alert(result); // Returns JSON OBject (Expected)
                alert(result["row"][0]["elements"][0]["distance"][0].text); //Returns undefined (Undesired)

            }
        };
        xhttp.open("POST", "includes/ajax/google_maps/get_distance_info.php", true);
        xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        xhttp.send("obj=" + dbParam);
}

The get_distance_info.php file is successfully called. It contains the following code:

header("Content-Type: application/json; charset=UTF-8");
$obj = json_decode($_POST["obj"], false);

$origin = $obj->origin;
$destination = $obj->destination;
$key = "[Removed for Stack Overflow]";

    $url = "https://maps.googleapis.com/maps/api/distancematrix/json?origins=".$origin."&destinations=".$destination."&mode=driving&language=en-EN&key=".$key;
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'APIKEY: [Removed for Stack Overflow]',
        'Content-Type: application/json',
     ));
     curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
   curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
    // curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); // These were tests
    // curl_setopt($ch, CURLOPT_PROXYPORT, 3128); // These were tests
    // curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0); // These were tests
    // curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); // These were tests
    $response = curl_exec($ch);
    curl_close($ch);
    echo $response;
    // echo json_encode($response); The result does not have to be re-encoded, as it is already encoded by the Google API.

Now the response I get from the get_distance_info.php file when I input two random addresses is the following:

{
   "destination_addresses" : [ "Great Tower St, London EC3R 5BT, UK" ],
   "origin_addresses" : [ "Eccles, Manchester M30 0NB, UK" ],
   "rows" : [
      {
         "elements" : [
            {
               "distance" : {
                  "text" : "346 km",
                  "value" : 345911
               },
               "duration" : {
                  "text" : "4 hours 7 mins",
                  "value" : 14818
               },
               "status" : "OK"
            }
         ]
      }
   ],
   "status" : "OK"
}

So the problem is that when we roll back to the first set of JavaScript code, I cannot get the text value of distance, it returns undefined. But you'll notice the attempt looks a little sloppy - this is due to the fact I've tried every conceivable variation, to the point I clearly cannot determine where I am wrong.

What I can determine, is that consistently, I cannot get past the "elements" object. It seems to not find it, and anything to do with it returns undefined.

Please, as I'm losing the plot; does anyone see where the problem with this code is, and how I can achieve the desired results?

To summarise: I want either the value of distance or the text of distance in the JSON object array, but am currently getting undefined.

P.s. for anyone wondering, if I uncomment out the json_encode, in my get_distance_info.php file, it simply returns as a string, and so any iterations are done on a per character basis rather than as an object.

Answer 1

It looks like you are looking for the first element of row:

alert(result["row"][0]["elements"][0]["distance"][0].text); //Returns undefined (Undesired)

However, I think the actual response contains 'rows' and distance is not an array.

Try:

alert(result["rows"][0]["elements"][0]["distance"].text);