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Editorial Team
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Asked: 2026-06-02T00:40:13+00:00

I use RegularExpressionValidator control to verify TextBox control named TextBox1, the web form in

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I use RegularExpressionValidator control to verify TextBox control named TextBox1, the web form in VS2003 Web application, like below:

<asp:TextBox id="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator id="RegularExpressionValidator1" runat="server" ErrorMessage="Fromat error."
 ValidationExpression="^(?=.*[0-9])(?=.*[a-zA-Z]).{8,10}$" ControlToValidate="TextBox1"></asp:RegularExpressionValidator>

When I input string “qwer1asd”, it does not match. But the same regular expression:

^(?=.*[0-9])(?=.*[a-zA-Z]).{8,10}$

…matches in JavaScript. How do I fix it?

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1 Answer

  1. Editorial Team

    Try this regex:

    ^(?=.{8,10}$)(?=.*[0-9])(?=.*[a-zA-Z]).+$

    There’s a bug in older versions of Internet Explorer (described here) that caused a regex like this to fail in the client even though it worked on the server. (That sounds like the opposite of what you’re describing, but I don’t see any other reason why your regex would fail.) Moving the length check to the first lookahead is the proven workaround for the bug.

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