Question

I have ‘little’ problem with javascript numbers and NaN.

I’m retrieving one single number via ajax POST method in JSON format.

$.post('test.php?a=b', {w: w}, function(json) {
    desktop.height = desktop.height - json.height * 2;
});

When I try to multiply it, it gives me NaN.

desktop.height = desktop.height - json.height * 2;
NaN

JSON IS an object, right? So when I enter this into firebug/chrome console, it gives me int 0, as expected.

var a = {}; a.t = 0; a.t * 2;
0

Even if I enter this into a console, it still gives me expected 0 int.

var a = {}; a.t = "0"; a.t * 2;
0

My question is, what’s going on and how do I fix it?

Answer 1

If the Content-Type header is not set to application/json from server and still If you want jQuery to parse the json String into JS object automatically then you have to add dataType json in $.post call.

$.post('test.php?a=b', {w: w}, function(json) {
    desktop.height = desktop.height - json.height * 2;
  },'json');

or you have to parse that youself using $.parseJSON like this

  $.post('test.php?a=b', {w: w}, function(json) {
     json = $.parseJSON(json);
     desktop.height = desktop.height - json.height * 2;
  });