How to use javascript to operate custom properties of web controls

During programming, custom properties of web server controls are sometimes used. For example, the TextBox control does not have the IsNotNull attribute, but we can add an IsNotNull attribute as a tag to facilitate programming.

Although the IDE will prompt the warning message "IsNotNull is not a TextBox property", it does not prevent us from using it!

Code:
<Asp: TextBox ID = "TextBox1" runat = "server" IsNotNull = "e"> </asp: TextBox>

Compile Javascript code:
Copy codeThe Code is as follows:
<Script language = javascript type = "text/javascript">
Function getClick ()
{
Var c = document. getElementById ("<% = TextBox1.ClientID %> ");
If (c. IsNotNull = 1)
{
Alert ("IsNotNull is 1 ");
}
Else if (c. IsNotNull = 0)
{
Alert ("IsNotNull is 0 ");
}
Else
{
Alert (c. IsNotNull); // if it is not 0 or 1, the attribute value of IsNotNull is displayed.
}
}
</Script>