If you use the Geolocation API, it would be as simple as using the following code.
navigator.geolocation.getCurrentPosition(function(location) {
console.log(location.coords.latitude);
console.log(location.coords.longitude);
console.log(location.coords.accuracy);
});
You may also be able to use Google’s Client Location API.
This issue has been discussed in Is it possible to detect a mobile browser’s GPS location? and Get position data from mobile browser. You can find more information there.