AJAX Callback and Javascript class variables assignments

Question

I am trying to build a little javascript class for geocoding addresses trough Google Maps API. I am learning Javascript and AJAX and I still can't figure out how can I initialize class variables trough a callback:

    // Here is the Location class, it takes an address and 
    // initialize a GClientGeocoder. this.coord[] is where we'll store lat/lng
    function Location(address) {
        this.geo = new GClientGeocoder();
        this.address = address;
        this.coord = [];                        
    }

    // This is the geoCode function, it geocodes object.address and 
    // need a callback to handle the response from Google
    Location.prototype.geoCode = function(geoCallback) { 
        this.geo.getLocations(this.address, geoCallback); 
    }

    // Here we go: the callback. 
    // I made it a member of the class so it would be able 
    // to handle class variable like coord[]. Obviously it don't work.
    Location.prototype.geoCallback = function(result) {
        this.coord[0] = result.Placemark[0].Point.coordinates[1];
        this.coord[1] = result.Placemark[0].Point.coordinates[0];
        window.alert("Callback lat: " + this.coord[0] + "; lon: " + this.coord[1]);
    }

    // Main
    function initialize() {
        var Place =  new Location("Tokyo, Japan");
        Place.geoCode(Place.geoCallback);
        window.alert("Main lat: " + Place.coord[0] + " lon: " + Place.coord[1]);
    }

    google.setOnLoadCallback(initialize);

Thank you for helping me out!

EDIT

Thanks TJ for your reply. I read your example and your post — things are getting much clearer. But I still have an issue. Have a look:

function bind(context, func) {
    return function() {
        return func.apply(context, arguments);
    }
}
function Location(address) {
    this.geo = new GClientGeocoder();
    this.address = address;
    this.coord = [];                        
}

Location.prototype.geoCode = function(callback) { 
    this.geo.getLocations(this.address, callback); 
}

Location.prototype.geoCallback = function(result) {
    this.coord[0] = result.Placemark[0].Point.coordinates[1];
    this.coord[1] = result.Placemark[0].Point.coordinates[0];
    // This alert is working properly, printing the right coordinates
    window.alert("I am in geoCallback() lat: " + this.coord[0] + "; lon: " + this.coord[1]);
}

function initialize() {
    var Place =  new Location("Tokyo, Japan");
    Place.geoCode(bind(Place, Place.geoCallback));
    window.alert("I am in initialize() lat: " + Place.coord[0] + "; lon: " + Place.coord[1]);
}

Why the alert in initialize() pops before the alert in geoCallback(), printing an undefined/undefined?