Simply by checking for it's disability. If it is disabled then skip validation else force to check.
Example:
function validateControls()
{
var txt=document.getElementById("<=txtboxName.ClientID%>");
if(txt.disabled==false)
{
if(txt.value.trim()=="")
{
return false;
}
else
{
return true;
}
}
}
Or,
Checking for the dropdownlist selected value.
Example:
function validateControls()
{
var drp=document.getElementById("<%=drpName.ClientID%>");
if(drp.value.trim()=="Other")
{
return false;
}
else
{
return true;
}
}
Hope, it helps :)