如何使用javascript基于asp.net中文本框中的文本启用/禁用Button。

<script language="javascript" type="text/javascript">
//function to enable button if two textboxes contains text
function SetButtonStatus(sender, target) {
var first = document.getElementById('<%=item_name.ClientId %>');
var second = document.getElementById('<%=model.ClientID %>');
var third = document.getElementById('<%=company.ClientId %>');
var fourth = document.getElementById ('<%=quantity.ClientId %>');
//Condition to check whether user enters text in two textboxes or not
if ((sender.value.length >= 1 && first.value.length >= 1) && (sender.value.length >= 1 && second.value.length >= 1) && (sender.value.length >= 1 && third.value.length >= 1) &&(sender.value.length >= 1 && fourth .value.length >= 1))
document.getElementById(target).disabled = false;
else
document.getElementById(target).disabled = true;
}</script>

这是我的代码，但收到错误

错误3'System.Web.UI.WebControls.TextBox'不包含'ClientId'的定义，并且没有可以找到接受类型'System.Web.UI.WebControls.TextBox'的第一个参数的扩展方法'ClientId'（你错过了使用指令或汇编参考吗？



请提出建议。

this is my code but getting an error
Error 3 'System.Web.UI.WebControls.TextBox' does not contain a definition for 'ClientId' and no extension method 'ClientId' accepting a first argument of type 'System.Web.UI.WebControls.TextBox' could be found (are you missing a using directive or an assembly reference?

please suggest something.