//set page event handlers for onload and unload
if (window.attachEvent) {
    window.attachEvent("onload", Page_Load);
    window.attachEvent("onunload", Page_Unload); 
} else {
    window.addEventListener("DOMContentLoaded", Page_Load, false);
    window.addEventListener("unload", Page_Unload, false);
}

function Page_Load() {
    initialiseMap();
}  

function Page_Unload() {
    if (map!=null) {
        //map.Dispose();
        map = null;
    }
}