Open a child window on Alloy/Titanium

child_window.js

$.child_window.open();

child_window.xml

<Alloy>
  <Window id="child_window">
    <Label>This is the Child Window</Label>
  </Window>
</Alloy>

parent.js

$.button.addEventListener('click', function(e) {
  child_window = Alloy.createController('child_window');
  // Since the controller calls the open() function, nothing
  // else is needed here
})

parent.xml

<Alloy>
  <Window id="parent_window">
    <Button id="button">Open Child Window</Button>
  </Window>
</Alloy>