How to return 3 closest locations from to users location using jQuery or JavaScript

In my mobile app, I've got users geolocation using the following code. I also have a geolocaion (latitude, longitude) of nearby cities. I can put the geolocation data of cities in array or SQLite database. How do I get and display the 3 closest cities near the users location using jQuery or JavaScript. I'm not using Google Maps.

$(document).ready(function() {
    var Geo={};

    if (navigator.geolocation) {
       navigator.geolocation.getCurrentPosition(success, error);
    }

    //Get the latitude and the longitude;
    function success(position) {
        Geo.lat = position.coords.latitude;
        Geo.lng = position.coords.longitude;
    }

    function error(){
        console.log("Geocoder failed");
    }

    function populateHeader(lat, lng){
        $('#myPopup').append('<p>Lattitude: ' + lat);
        $('#myPopup').append('<br />Longitude: ' + lng + '</p>');
    }
});

Thanks

Joe