JQuery.getJson isn't triggered properly - php

Question

I am trying to use JSON for getting dynamic content to my webpage, using javascript. Something is not correct and I have problem figuring out what it can be. In firebug I can see that the JSON-data is retreived as it should. When looking in Firebug under "DOM", the URL I am accessing for the page (the actual page I have created, not the URL to JSON-data) is coloured red (see screenshot below). Here is my javascript:
$(document).ready(function() {
$('#target').click(function() {
alert("At least I',m reached ");
$.getJSON('http://localhost/timereporting/phpscriptlibrary/get_remaining_hours.php', function(data) {
document.getElementById('errorDiv').innerHTML = "Divtext";
alert("Inside getJason");
});
alert("At least I',m done ");
});
This is the significant part of my php file:
$json_string = "{\"activities\": ";
$json_string = $json_string."[";
for ( $counter = 0; $counter < $num; $counter += 1) {
$json_string = $json_string."[".mysql_result($rows,$counter,'date').", \"".mysql_result($rows,$counter,'activity_id')."\", ".mysql_result($rows,$counter,'hours')."]";
if($counter != ($num-1)){
$json_string = $json_string.", ";
}
}
$json_string = $json_string."]}";
echo $json_string;
I assume that "echo" is the way to "send" the JSON-data to the javascript?
One strange thing is that in firebug the JSON-data is presented in two different ways. If you look at the included screenshots below, the second one has dates like "1988" or similar while on the first one the dates are more complete like "2010-12-10". The first screenshot depicts how it should be and that's how I am trying to send it, and obviously it is received like this at some point.
How come my div-tag isn't updated with the date or that the alert inside the $.getJSON isn't triggered, only the alert before and after?

Answer 1

You don't create your JSON strings properly. Every string has to be enclosed in double quotes. But 2010-12-10 is not and jQuery evaluates this as 2010 - 12 - 10 = 1988.
Don't build your string manually, use json_encode, something like:
$data = array();
while(($row = mysql_fetch_array($result))) {
$data[] = array($row['date'], intval($row['activity_id']), intval($row['hours']));
}
echo json_encode(array('activities' => $data));