<body>
<select size="3" id="sel">
<option disabled>Выберите героя</option>
<option value="1">Чебурашка</option>
<option selected value="2">Крокодил Гена</option>
<option value="3">Шапокляк</option>
</select>
<input id="test" type="button" value="Test"/>
<script>
function version1() {
alert('version1');
test.onclick = func1;
}
function version2() {
alert('version2');
test.onclick = func2;
}
function version3() {
alert('version3');
test.onclick = func3;
}
sel.onchange = function () {
window['version' + this.value]();
}
function func1(){alert('func1')}
function func2(){alert('func2')}
function func3(){alert('func3')}
</script>
</body>