how to add javascript on custom control(server control)

Question

1.00/5 (1 vote)

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	<asp:Label ID="Label1" runat="server" Text="first number">	<asp:TextBox ID="txtfnumber" runat="server">

	<asp:Label ID="Label2" runat="server" Text="second number">	<asp:TextBox ID="txtsnumber" runat="server">
	<asp:Button ID="btncalculate" runat="server" OnClientClick="add()" Text="Add" />	<asp:Label ID="lblResult" runat="server">

ERROR message is shown

JavaScript runtime error: Unable to get property 'value' of undefined or null reference

Posted 20-Aug-15 19:55pm

manish-gusain8909

Updated 20-Aug-15 20:33pm

v2

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Comments

Sergey Alexandrovich Kryukov 21-Aug-15 2:03am

It sounds extremely trivial, and not really a question. What have you tried so far?
—SA

3 solutions

Solution 1

See this example:
Add the below code on your custom control.

HTML

<p>Click the button to calculate x.</p>
    <button >Try it</button>
    <br />
    <br />Enter first number:
    <input type="text" id="txt1" name="text1">Enter second number:
    <input type="text" id="txt2" name="text2">
<p id="demo"></p>//replace this p tag with your label</input></input>

JavaScript

<script type="text/javascript">
  function myFunction() {
    var y = document.getElementById("txt1").value;
    var z = document.getElementById("txt2").value;
    var x = +y + +z;
    document.getElementById("demo").innerHTML = x;
  }
</script>

Posted 20-Aug-15 20:06pm

Sanket Saxena

v3

Solution 3

If you are using master pages concept, for getting any control value use
stno = document.getElementById("<%=txtfnumber.ClientID%>").value;

Otherwise you can get directly by using
stno = document.getElementById("txtfnumber").value;

Posted 20-Aug-15 21:55pm

Member 10239127

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F-ES Sitecore · Accepted Answer · 2015-08-20T21:14:00

Solution 2

JavaScript runs on the client, your aspx files are on the server. This code

stno = document.getElementById("txtfnumber").value;

is looking for an element with an id of "txtfnumber". Your aspx page has a server tag with that ID, but javascript uses what is sent to the browser, so view the source of the page and see if there is an element in the source with that ID. asp.net changes the IDs of your controls in various situations so you need to use .net to generate the right ID in your javascript.

stno = document.getElementById("<%=txtfnumber.ClientID%>").value;

Posted 20-Aug-15 21:14pm

F-ES Sitecore

Comments

manish-gusain8909 21-Aug-15 4:11am

thanks your code worked. kindly explain why it is

F-ES Sitecore 21-Aug-15 4:17am

.net needs to alter your IDs to ensure they are unique, and the ClientID property lets your code know what the id of that component will be when it is rendered as html. View the source of the page and look at your element tags and look at the javascript and it should become clear.

manish-gusain8909 21-Aug-15 8:10am

thanks .now i understood clearly