appcelerator_passing_data_app.js

var common = { value: "123", title: "None" };
 
var tabGroup = Titanium.UI.createTabGroup();
 
for(var i = 0; i < 2; ++i) {
    var win = Titanium.UI.createWindow({
        title : "Test #" + i,
        backgroundColor: '#fff',
        url: "tab.js"
    });
    win.common = common;
 
    var tab = Titanium.UI.createTab({
        title: "Test " + i,
        window: win
    });
 
    tabGroup.addTab(tab);
}
 
tabGroup.open();

appcelerator_passing_data_tab.js

var win = Titanium.UI.currentWindow,
    common = win.common;
 
var field;
 
field = Titanium.UI.createTextField( {
    value : "",
    width : 90, height : 30, left: 10, top: 10,
    borderStyle : Titanium.UI.INPUT_BORDERSTYLE_ROUNDED
});
 
win.add(field);
 
win.addEventListener('focus', function(e) {
    Ti.API.info('focus updating value: value=' + common.value + " title=" + common.title);
    field.value = common.value;
    common.title = win.title;
    Ti.API.info('Now, value=' + common.value + " title=" + common.title);
});
 
win.addEventListener('blur', function(e) {
    Ti.API.info('blur check: field=' + field.value + ' value=' + common.value + " title=" + common.title);
});
 
field.addEventListener('change', function(e) {
    Ti.API.info('field changed value to ' + e.value);
    common.value = e.value;
    Ti.API.info('After update, value=' + common.value + " title=" + common.title);
});

Does not seem to work... Seems the common object is passed by value, not by reference as can be seen in the debug log:

[INFO] focus updating value: value=123 title=None
[INFO] Now, value=123 title=Test #0
[INFO] field changed value to 123a
[INFO] After update, value=123a title=Test #0
[INFO] blur check: field=123a value=123a title=Test #0
[INFO] focus updating value: value=123 title=None
[INFO] Now, value=123 title=Test #1