ASP.NET Javascript 运行时错误

Question

I have just started a new ASP.NET web application and I am totally new to everything and after moving a few things round I have been getting this error and I don't understand what it means.

It happens when I go to enter anything in the Password box.

Could someone please help me out on this issue.

EDIT:

    <li>
        <asp:Label runat="server" AssociatedControlID="Password">Password</asp:Label>
        <asp:TextBox runat="server" ID="Password" TextMode="Password" onkeypress="capLock(event)" />
        <asp:RequiredFieldValidator runat="server" ControlToValidate="Password" CssClass="field-validation-error" ErrorMessage="The password field is required." />
    </li>

Answer 1

document.getElementById("divMayus") is returning null or undefined.

You should look at the rendered html and find the div that you are trying to reference to make sure the id is the same as you are trying to reach. Asp.net alters the ids of server controls depending on their containers. So if you moved stuff around, the id may have also been changed.

Answer 2

Try to do that inside

window.onload = function(){
  // code goes here
}

I think you are trying to access DOM even before it is being created.

the document.getElementById('divMayus') is undefined