Aşağıdaki Kodda 3 Adet Select Var Ve 3 Selectinde Aynı Anda Seçili Olduğu Verilerin Toplama İşlemini Yapıp Göstermesini Nasıl Sağlarım
<!DOCTYPE html>
<html>
<body>
<p>Choose an option in the drop-down list and display that option.</p>
<form>
<select id="mySelect1" onchange="myFunctiona()">
<option>+1</option>
<option>+2</option>
<option>+3</option>
<option>+4</option>
</select>
</form>
<form>
<select id="mySelect2" onchange="myFunctionb()">
<option>+10</option>
<option>+20</option>
<option>+30</option>
<option>+40</option>
</select>
</form>
<form>
<select id="mySelect3" onchange="myFunctionc()">
<option>+100</option>
<option>+200</option>
<option>+300</option>
<option>+400</option>
</select>
</form>
<p id="demo"></p>
<script>
function myFunctiona() {
var x = document.getElementById("mySelect1");
var i = x.selectedIndex;
document.getElementById("demo").innerHTML = x.options[i].text;
}
</script>
</body>
</html>