dropdownlist validation javascript

Question

im use this validation to all dropdown list but javascript validation not work so please help me 

 

 

 

function ValidateDropDownList() {

if (ddlst.value.length == State) {

alert("Please Select States.");

ddlst.focus();

return false;

}

if (document.getElementById("<%=ddlmo.SelectedIndex %>").value == "0")

{

alert("Please Select Month.");

document.getElementById("<%=ddlmo.SelectedIndex %>").focus();

return false;

}

if (ddlye.value.length >= 0) {

alert("Please Select Year.");

ddlye.focus();

return false;

}

if (ddltr1.value.length >= 0) {

alert("Please Select Tax Revenue.");

ddltr1focus();

return false;

}

if (ddlntr1.value.length >= 0) {

alert("Please Select Non-Tax Revenue.");

ddlmo.focus();

return false;

}

if (txtncs.value.length <= 0) {

alert("Please Select Net Contribution To State.");

txtncs.focus();

return false;

}

if (isNaN(txtncs.value)) {

alert("Net Contribution To State should be numeric!");

txtncs.focus();

return false;

}

}

</script>