Access GET directly from JavaScript?

Look at

window.location.search

It will contain a string like this: ?foo=1&bar=2

To get from that into an object, some splitting is all you need to do:

var parts = window.location.search.substr(1).split("&");
var $_GET = {};
for (var i = 0; i < parts.length; i++) {
    var temp = parts[i].split("=");
    $_GET[decodeURIComponent(temp[0])] = decodeURIComponent(temp[1]);
}

alert($_GET['foo']); // 1
alert($_GET.bar);    // 2

Here's another idea:

<script type="text/javascript">

var $_GET = <?php echo json_encode($_GET); ?>;

alert($_GET['some_key']);
// or
alert($_GET.some_key);

</script>