Using JavaScript to save roundtrips

Client code to set a check box to true when the user types a search string into a text box without having to make a roundtrip to the server.

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As part of a recent project, it was necessary to set a check box to true, when the user typed a search string into the text box. This would have required at least one roundtrip to the server, which would have had a server impact on the application responsiveness, unless some client code was used. The code example below shows how this was done using JavaScript. Note the JavaScript and the ASP.NET code to invoke the function via "onkeyup." The "onkeyup" is CASE sensitive.

Code:

<%@ Page Language="vb" AutoEventWireup="false" Codebehind="DEMO.aspx.vb"
Inherits="Probe.DEMO"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
  <HEAD>
    <title>DEMO</title>
    <meta name="GENERATOR" content="Microsoft Visual Studio.NET 7.0">
    <meta name="CODE_LANGUAGE" content="Visual Basic 7.0">
    <meta name="vs_defaultClientScript" content="JavaScript">
    <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
    <script language="javascript">
    function txtFredChange() { var theform = document.Form1;
  theform.chkFred.checked =1;    }    
    &tl;/script>  
  </HEAD>
  <body>
    <form id="Form1" method="post" runat="server">
      <asp:TextBox id="txtFred" onkeyup="txtFredChange()"
runat="server"></asp:TextBox>
      <asp:CheckBox id="chkFred" runat="server" Text="Select using
this"></asp:CheckBox>
    </form>
  </body>
</HTML>

This was first published in April 2003

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