无法使用Java脚本验证文本框

Question

my input text box source like this:

<asp:TextBox ID="TxtDepCode" runat="server" Height="18px"></asp:TextBox>

and my javascript function like this:

  <script type="text/javascript" language="javascript">
    function confirm_user() {
        var userPass = document.getElementById('TxtDepCode');
        alert(userPass)
        if (userPass=''){
        alert("value is blank")
        }
        if (confirm("Department already available, would you like to update ?") == true)
            return true;
        else
            return false;
    }
</script>

in submit button click i want to check wethar corresponding text is empty or not my submit button click event like this:

Answer 1

var userPass = document.getElementById('TxtDepCode').value;

Or

var userPass = document.getElementById('<%=TxtDepCode.ClientID%>').value;

Modify the first line of function to get value of textbox as above

if (userPass==''){

Modify if as above

Answer 2

The crucial issues in the code are as follows:

1. Get the value of the password and not the element:

   var userPass = document.getElementById('TxtDepCode').value;

2. Change the if to == or === instead of single =

   if (userPass == '') {

3. You are using <asp:TextBox> that can have a dynamic ID. Therefore you should get the dynamic ID using .NET's ClientID :

   var userPass = document.getElementById('<% =TxtDepCode.ClientID %>').value;

Answer 3

You need to return false if value is blank too

<script type="text/javascript" language="javascript">
function confirm_user() {
    var userPass = document.getElementById('TxtDepCode');
    alert(userPass)
    if (userPass.value == ''){ // == not = and userPass.value
    alert("value is blank");
    return false; // Need to stop the function
    }
    if (confirm("Department already available, would you like to update ?") == true)
        return true;
    else
        return false;
}