Put something like this in your HTML file:
<a href="#" onClick="closeMeNow();" data-role="button">Close App</a>
This is a link to such a function in your JS file:
function closeMeNow() { navigator.app.exitApp(); }
I know that the syntax is more JQM than Sencha, but since the concept is basically the same, you can simply edit where necessary.
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