I needed a way to determine the current user's location as near as possible so I could produce valid results from Foursquare's suggestCompletion API.

Current User Location with fallbacks

//get user's location
var latlong;

if(navigator.geolocation) {
	//try with HTML5
		
	function showPosition(position){
    
    		var htmllat = position.coords.latitude;
        	var htmllon = position.coords.longitude;
        
        if(htmllat && htmllon){
	        latlong = htmllat+','+htmllon;
		console.log('Location determined using HTML5');
	    }
    }
    navigator.geolocation.getCurrentPosition(showPosition);
}
        
if(!latlong){
	//All of my users are using a form within one of our sites which may or may not have a group location available.  I've put that saved lat/long into a hidden HTML div
	var savedlat = $('#group_loc span#group_lat').text();
	var savedlon = $('#group_loc span#group_long').text();
	
	if(savedlat && savedlon){
		latlong = savedlat+','+savedlon;
		console.log('Location determined using saved chapter location');
	}
}

if(!latlong){
	//if no group location, try external IP lookup using MaxMind js -> http://dev.maxmind.com/geoip/
	var geolat = geoip_latitude();
	var geolon = geoip_longitude();
	
	if(geolat && geolon){		
		latlong = geolat+','+geolon;
		console.log('Location determined using GeoIP lookup');
	}
}				

if(!latlong){
	//final fallback is the geographic center of the US. Hopefully it doesn't come to this.
	latlong = "39.8282,-98.5795"
    console.log('Unable to determine location');
}