Hi,
i did some code for your requirement
check this once
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script language ="javascript" >
function check1(tid) {
var len = document.getElementById("DropDownList2").options.length;
var j = 0;
for (var i = 0; i < len; i++) {
if (document.getElementById("DropDownList2").options[i].value == document.getElementById(tid).value) {
j = i;
}
}
document.getElementById("DropDownList2").options[j].disabled = "disabled";
}
function check2(tid) {
var len = document.getElementById("DropDownList3").options.length;
var j = 0;
for (var i = 0; i < len; i++) {
if (document.getElementById("DropDownList3").options[i].value == document.getElementById(tid).value) {
j = i;
}
}
document.getElementById("DropDownList3").options[j].disabled = "disabled";
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:dropdownlist id="DropDownList1" runat="server" onchange="check1(this.id)" xmlns:asp="#unknown">
<asp:listitem text="first" value="first"></asp:listitem>
<asp:listitem text="second" value="second"></asp:listitem>
<asp:listitem text="third" value="third"></asp:listitem>
<asp:listitem text="fourth" value="fourth"></asp:listitem>
</asp:dropdownlist>
<asp:dropdownlist id="DropDownList2" runat="server" onchange="check2(this.id)" xmlns:asp="#unknown">
<asp:listitem text="first" value="first"></asp:listitem>
<asp:listitem text="second" value="second"></asp:listitem>
<asp:listitem text="third" value="third"></asp:listitem>
<asp:listitem text="fourth" value="fourth"></asp:listitem>
</asp:dropdownlist>
<asp:dropdownlist id="DropDownList3" runat="server" xmlns:asp="#unknown">
<asp:listitem text="first" value="first"></asp:listitem>
<asp:listitem text="second" value="second"></asp:listitem>
<asp:listitem text="third" value="third"></asp:listitem>
<asp:listitem text="fourth" value="fourth"></asp:listitem>
</asp:dropdownlist>
</div>
</form>
</body>
</html>
I hope you understood what I did
All the Best
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