How to Retrieve a Zipcode Using JavaScript

[codesyntax lang="javascript"]// Retrieve user’s Zipcode
// Demo
            at http://sandbox.gtaero.net/zipcode.html
function retrieve_zip(callback)
{

            try { if(!google) { google = 0; } } catch(err) { google = 0; } // Stupid Exceptions

            if(navigator.geolocation) // FireFox/HTML5 GeoLocation
 {

            navigator.geolocation.getCurrentPosition(function(position)
 {

            zip_from_latlng(position.coords.latitude,position.coords.longitude,callback);
 });
 }

            else if(google && google.gears) // Google Gears GeoLocation
 {
 var geloc =
            google.gears.factory.create('beta.geolocation');
 geloc.getPermission();

            geloc.getCurrentPosition(function(position)
 {

            zip_from_latlng(position.latitude,position.longitude,callback);
 },function(err){});
 }
}
function
            zip_from_latlng(latitude,longitude,callback)
{
 // Setup the Script using Geonames.org's
            WebService
 var script = document.createElement("script");
 script.src =
            "http://ws.geonames.org/findNearbyPostalCodesJSON?lat=" + latitude + "&lng=" + longitude + "&callback="
            + callback;
 // Run the Script

            document.getElementsByTagName("head")[0].appendChild(script);
}
function
            example_callback(json)
{
 // Now we have the data! If you want to just assume it's the
            'closest' zipcode, we have that below:
 zip = json.postalCodes[0].postalCode;
 country =
            json.postalCodes[0].countryCode;
 state = json.postalCodes[0].adminName1;
 county =
            json.postalCodes[0].adminName2;
 place = json.postalCodes[0].placeName;
 alert(zip);
}
retrieve_zip("example_callback");
            // Alert the User's Zipcode
[/codesyntax]