How to find the selected radio button immediately using the 'this' variable?

<script>

function favAnimal(button) {

alert('You like '+button.value+'s.');

}

</script>

<input type="radio" name="marsupial" value="kangaroo"

onchange="favAnimal(this)">Kangaroo

<br /><input type="radio" name="marsupial" value="Opossum"

onchange="favAnimal(this)">Opossum

<br /><input type="radio" name="marsupial" value="Tasmanian Tiger"

onchange="favAnimal(this)">Tasmanian Tiger