Disable a Button if non numeric characters are entered

Here's a scenario. You have to accept only numeric characters from the user in a textbox. If the user types in anything other than a numeric character, then the submit button should be disabled.

To achieve this requirement we can use JavaScript and the OnKeyUp event as shown below:

Script

<head runat="server">

<title></title>

<script type="text/javascript">

function CallScript(sender, btn) {

var chkDigit = /^\d+$/;

    if (chkDigit.test(sender.value)) {

        document.getElementById(btn).disabled = false;

    }

    else {

        document.getElementById(btn).disabled = true;

    }

}

</script> 

</head>

<body>

<form id="form1" runat="server">

<div>

    <asp:TextBox ID="TextBox1" runat="server"/>

    <asp:Button ID="Button1" runat="server" 

    Text="Submit" Enabled="false" />

</div>

</form>

</body>

</html>

To register the OnKeyUp with the TextBox use the following code:

C#

    protected void Page_Load(object sender, EventArgs e)

    {

        TextBox1.Attributes.Add("onKeyUp", "CallScript(this,'Button1')");

    }

VB.NET

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

        TextBox1.Attributes.Add("onKeyUp", "CallScript(this,'Button1')")

    End Sub

If you are using this script in a MasterPage, make sure to use Button1.ClientID

Note: Watch for the Copy and Paste scenarios where you will need to use the TextChangedEvent.

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About The Author

Suprotim Agarwal, ASP.NET Architecture MVP works as an Architect Consultant and provides consultancy on how to design and develop Web applications.

Suprotim is also the founder and primary contributor to DevCurry, DotNetCurry and SQLServerCurry. He has also written an EBook 51 Recipes using jQuery with ASP.NET Controls.

Follow him on twitter @suprotimagarwal