how to extract information from JSON using jQuery

Question

I have a JSON response that is formatted from my C# WebMethod using the JavascriptSerializer Class . I currently get the following JSON back from my query:

{"d":"[{\"Lat\":\"51.85036\",\"Long\":\"-8.48901\"},{\"Lat\":\"51.89857\",\"Long\":\"-8.47229\"}]"}

I'm having an issue with my code below that I'm hoping someone might be able to shed some light on. I can't seem to get at the information out of the values returned to me. Ideally I would like to be able to read in the Lat and Long values for each row returned to me.

Below is what I currently have:

$.ajax({
                    type: "POST",
                    url: "page.aspx/LoadWayPoints",
                    data: "{'args': '" + $('numJourneys').val() + "'}",
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: function (msg) {
                        if (msg.d != '[]') {
                            var lat = "";
                            var long = "";
                            $.each(msg.d, function () {
                                lat = this['Lat'];
                                long = this['Long'];
                            });
                            alert('lat =' + lat + ', long =' + long);
                        }
                    }
                });

I think the issue is something to do with how the JSON is formatted but I might be incorrect. Any help would be great.

Thanks, Rich

Answer 1

What's happening is you're getting JSON encoded inside a string within your JSON. It's redundant, but there is a solution without changing your output method.

To handle this, jQuery has a JSON parser ( $.parseJSON() ) you can use do parse the string inside the response.

So I believe you would do it like this:

$.ajax({
  type: "POST",
  url: "page.aspx/LoadWayPoints",
  data: "{'args': '" + $('numJourneys').val() + "'}",
  contentType: "application/json; charset=utf-8",
  dataType: "json",
  success: function(msg) {
    if (msg.d != '[]') {
      var content = $.parseJSON(msg.d);

      var lat = "";
      var long = "";
      $.each(content, function() {
        lat = this['Lat'];
        long = this['Long'];
      });
      alert('lat =' + lat + ', long =' + long);
    }
  }
});

Answer 2

Looks like your JSON is incorrectly built:

{"d":"[{\"Lat\":\"51.85036\",\"Long\":\"-8.48901\"},{\"Lat\":\"51.89857\",\"Long\":\"-8.47229\"}]"}

Probably should be:

{"d":[{"Lat":"51.85036","Long":"-8.48901"},{"Lat":"51.89857","Long":"-8.47229"}]}

Notice the {"d":"..."} ? looks like your "d" points to a string, not an array.

Answer 3

Please try this:

 $.each(msg.d, function () {
                                lat = this['Lat'];
                                long = this['Long'];
                            });

After going through the JSON there is no MapLatPosition or MapLongPosition

HTH

Answer 4

I think you need something like that:

$.ajax({
    type: "POST",
    url: "page.aspx/LoadWayPoints",
    data: "{'args': '" + $('numJourneys').val() + "'}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function (msg) {
        $.each(msg.d, function () {
            var lat = "";
            var long = "";
            lat = this.Lat; // Lat/Long this is how you called it in your JSON responce
            long = this.Long;
            alert('lat =' + lat + ', long =' + long);
        });
    }
});

hope it helps

• also, as xyld mentioned above, look at your JSON