javascript - Accessing controls in Master page from content page - Stack Overflow

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I am trying to access control in Master page from Content page(Asp) using javascript like this

alert(document.getElementById('<%=((Label)Master.FindControl("lbl")).ClientID %>').value);

control in Master page is as follow,

 <asp:Label ID="lbl" runat="server" Text="one"></asp:Label>

But unfortunately it is not working. I am getting undefined value

I am trying to access control in Master page from Content page(Asp) using javascript like this

alert(document.getElementById('<%=((Label)Master.FindControl("lbl")).ClientID %>').value);

control in Master page is as follow,

 <asp:Label ID="lbl" runat="server" Text="one"></asp:Label>

But unfortunately it is not working. I am getting undefined value

• javascript
• asp
• master-pages
• content-pages

Share Improve this question Follow edited Mar 12, 2014 at 17:34 user3411907 asked Mar 12, 2014 at 17:22 user3411907user3411907 2111 gold badge11 silver badge44 bronze badges 5

• In what way is it not working? Do you get an Exception from .NET or an undefined value in the alert? The FindControl() method is not recursive, so unless your lbl control is a direct children of Master, it won't be found. – juan.facorro Commented Mar 12, 2014 at 17:26
• so what is the solution? how can I correct it? – user3411907 Commented Mar 12, 2014 at 17:29
• I get undefined value – user3411907 Commented Mar 12, 2014 at 17:33
• Why you don't use a pure javascript solution? jQuery helps you a lot: $("#parent").find(".contrl-class-name").val(); . If you give us more information, we'd give you better answer. – Maysam Commented Mar 12, 2014 at 17:34
• I know it works, I have worked on project where it's working fine. I am just missing something that's why I asking for help – user3411907 Commented Mar 12, 2014 at 17:38

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5 Answers 5

Sorted by: Reset to default 3

I noticed that you are actually accessing the .value field of the element that the <asp:Label /> control generates, which is a <span></span>. This type of element won't return anything for the .value attribute. If you are actually trying to access its text then use:

alert(document.getElementById('<%=((Label)Master.FindControl("lbl")).ClientID %>').innerText);

or

alert(document.getElementById('<%=((Label)Master.FindControl("lbl")).ClientID %>').innerHTML);

The problem is that a master page is a naming container, hence the client id of the control receives a prefix which is the id of the naming container. Using JavaScript, it is easily solvable:

var elm = document.querySelector('[id$="lbl"]');

$= means, ends with.

Include jQuery in your page and use this script:

<script>
$(document).ready(function(){
    alert($("#lbl").text());
});
</script>

This is work for me:(Check the below code)

alert(document.getElementById('<%=(Master.FindControl("lbl")).ClientID %>').innerText);

Using getElementById didn't work for me. The following can be used instead:

$find('<%=((Label)Master.FindControl("lbl")).ClientID %>');

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