$.getJSON not working with simple PHP Script - php

Question

The JS doesn't work with the PHP script. I get no response.
Here's the PHP script:
<?php
$a = array('data' => 'Hello');
echo json_encode($a);
?>
Here is the JQuery Script:
function getCityAndState(data, location)
{
var jsonString = {"zipCode": data};
var outR = outputResults
alert("JSON String:" + jsonString.zipCode);
if (location === "living")
{
$("#livingCityField").val("");
$("#livingStateField").val("");
alert("Inside getCityAndState: " + location);
//$.get("testfile.php",
// {zipCode: data},
// outR,
// 'text'
// );
$.getJSON("testfile.php",function(d) {
alert("JSON Data: " + d.data);
});
}
What am I doing wrong?
alert("Inside getCityAndState: " + location); does execute as expected but otherwise nothing happens. There is no exception thrown, no error message, nothing. It doesn't return any data at all.
I'm using Aptana 2 as an IDE, in case that makes a difference.

Answer 1

Your PHP script is missing the Header, it should be something like:
<?php
header('Content-type: text/json'); //added line
$a = array('data' => 'Hello');
echo json_encode($a);
?>

Answer 2

The second parameter of jQuery's $.getJSON() function isn't the callback that returns the data, it is supposed to be a map or string containing additional data to be sent to the server. The callback function is the third parameter.
I didn't test this, but it should be something along these lines:
$.getJSON('ajax/test.json', "", function(data, textStatus, jqXHR){
//In here you should have access to the data return by the server thourgh the "data" variable.
});
EDIT: As very well pointed out by #Rocket and #Tadeck, optional arguments can be omitted and "rearranged" since jQuery checks the argument's type. This is the case with the second and third arguments of the getJSON() function.
Given that, and although this shouldn't be the source of the problem, it makes sure the function receives all the arguments in the expected order, and it should yield the same result as omitting the second parameter.
Documentation: http://api.jquery.com/jQuery.getJSON/