view.js

function do_something(e) {
  if (e.source.type == 'a') {
    // something specific to a
  }
  else if (e.source.type == 'b') {
    // something specific to b
  }
}

view.xml

<Alloy>
  <View>
    <Button id="button1" type="a" onClick="do_something"/>
    <Button id="button2" type="a" onClick="do_something"/>
    <Button id="button3" type="b" onClick="do_something"/>
  </View>
</Alloy>