Some time, we have a situation to access the server side
ASP.Net controls and its values using Client side script like java script. In this post I’m going to explain how to do
that with a simple example.
A word about Client ID:
As all of us know, that server side controls are submitted
and processed by the ASP.Net engine, which emits the respective HTML to the
browser. At that time the ASP.Net engine takes the server controls and provide
ID (which can be varied across asp.net versions) for it.
Consider the below example, which has 3 text boxes, after
entered values in first 2 text boxes when the user clicks the button then javascript
function called which will add the values and put it in 3rd text
box. These controls are Server controls.
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript">
function Add() {
var intFirstNo = document.getElementById("<%= txtFirstNo.ClientID %>").value;
var intSecondNo = document.getElementById("<%= txtSecondNo.ClientID %>").value;
var intResult = parseInt(intFirstNo) + parseInt(intSecondNo);
document.getElementById("<%= txtResult.ClientID %>").value = intResult;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<table>
<tr>
<td>
Enter First Number:
</td>
<td>
<asp:textbox clientidmode="Predictable" id="txtFirstNo" runat="server"></asp:textbox>
</td>
</tr>
<tr>
<td>
Enter Second Numer:
</td>
<td>
<asp:textbox id="txtSecondNo" runat="server"></asp:textbox>
</td>
</tr>
<tr>
<td>
Addition is:
</td>
<td>
<asp:textbox id="txtResult" runat="server"></asp:textbox>
</td>
</tr>
<tr>
<td align="center" colspan="2">
<asp:button id="btnResult" onclientclick="Add(); return false;" runat="server" text="Calculate">
</asp:button></td>
</tr>
</table>
</form>
</body>
</html>
Consider this java script line:var intFirstNo = document.getElementById("<%= txtFirstNo.ClientID %>").value;
When the above line is read by the ASP.Net engine, it will search the Server control ID “txtFirstNo” and get the
respective client ID, which has been assigned by ASP.Net engine. In other words, ASP.Net get the Client ID for
that Server control “txtFirstNo” and substitute there in between the double
quotes. As a result when we saw the view source of the page we can read that
above one as follows:
var intFirstNo = document.getElementById("txtFirstNo").value;
We also return false (in line no 42) after call the javascript function "Add" to avoid the postback when we click the button.
Just copy the above sample in a webform and try it yourself!
Please leave your valuable comment which improves every Article!
Hope this helps a bit!
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