Later we will rewrite the weather widget once again to get the weather from a web service instead of a static file on the server. We want to show the user the weather for their current location, so we need some way to determine where the user is. HTML5 has just the thing for that: the Geolocation API.
Geolocation is widely supported by nearly every modern browser. The accuracy of the location depends on the capabilities of the user's device. Devices that have GPS will give you a very accurate location, while those that don't will try to determine the user's location as close as they can by some other means, such as by IP address.
The Geolocation API is accessed by using the navigator.geolocation object. To get the user's location you call the getCurrentPosition() method. It takes two parameters- a callback function if it succeeds and a callback function if it fails:
navigator.geolocation.getCurrentPosition(
function(position) { alert("call was successful"); },
...