<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