Use haversine to calculate the distance in miles between two lat-long points.

haversine-miles.js

/*	Modified from http://stackoverflow.com/questions/14560999/using-the-haversine-formula-in-javascript	*/

function toRad(v){return v * Math.PI / 180;}
function kmToMiles(km) {return (km * 0.62137).toFixed(2);}

var l1	=	LatLong(0,0);
var l2	=	LatLong(0,0);

function LatLong(lat, lon) {
	return {Latitude: lat, Longitude: lon}
}

function haversine(l1, l2) {
	var R = 6371; // km 
	var x1 = l2.Latitude-l1.Latitude;
	var dLat = toRad(x1);  
	var x2 = l2.Longitude-l1.Longitude;
	var dLon = toRad(x2);  
	var a = Math.sin(dLat/2) * Math.sin(dLat/2) + 
			Math.cos(toRad(l1.Latitude)) * Math.cos(toRad(l2.Latitude)) * 
			Math.sin(dLon/2) * Math.sin(dLon/2);  
	var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
	var d = R * c;
	return d;
}

alert(kmToMiles(haversine(l1, l2))+' miles');