function onLoad() {
    alert("hjk");     // This is working
    document.addEventListener("deviceready", onDeviceReady, false);
}

// Cordova is loaded and it is now safe to call Cordova methods
function onDeviceReady() {
    // Register the event listener
    alert("hjkj,j");       // This is also working
    document.addEventListener("backbutton", onBackKeyDown, false);
}

// Handle the back button
function onBackKeyDown() {
    alert("hi");     // This is not working, why??
    Ext.getCmp('aboutcards').setActiveItem('card-0');
}