Get current location Lat Long

Is sending me status code 500 on requset....

Your var_dump() call will output to AJAX response. You can see the output in Firebug or Chrome console.

Also you can get the response in JS:

$.post("map.php", {lat: lat, lng: lng}, function(response) {
alert(response);
}, "text");

Ok but i need those coordinate ($lat , $lng) for selecting from my database via PHP. I need to put them in MySql query so alert(); will not help me....

You can use $lat and $lng in your PHP code as you like.
However all output (echo, print, var_dump, etc.) will go to AJAX response.