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Editorial Team
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Asked: 2026-05-15T10:01:31+00:00

On load I’m both calling a JavaScript setTimeout() function that will hide a .NET

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On load I’m both calling a JavaScript setTimeout() function that will hide a .NET Panel control, and hiding it in the code behind on first load. Clicking the save button will set the Panel to visible then reload the page at which point a setTimeout() function is called… so basically you click save, and see a panel with “Details Saved” for three seconds, at which point it disappears.

The problem is the external JavaScript file can’t find _pDivAlert.ClientID (I’ve debugged and it returns null). It only works when the code is in a tag in the .aspx page. Any suggestions as to how I can either pass the client ID to the HideControl() function or find the ClientID from the external JS file?

Here’s my code, any suggestions? 

<script language="javascript" src="Forms.js" type="text/javascript"></script>

<body onload="ToggleAlert()">
<form id="form1" runat="server">
<script type="text/javascript">
    //alert the user that the details were saved
    function HideControl() {
        var control = document.getElementById('<%=_pDivAlert.ClientID %>');
        if(control != null)
            control.style.display = 'none';
    }
    function ToggleAlert() {
        setTimeout("HideControl()", 3000);
    }
</script>

I’ve also tried sending the ClientID within the ToggleAlert() call, but that didn’t work:

<body onload="ToggleAlert('<%=_pDivAlert.ClientID %>')">

External JS:

function HideControl(_c) {
var control = _c;
if (control != null)
    control.style.display = 'none';
}
function ToggleAlert(_c) {
    setTimeout("HideControl(_c)", 3000);
}
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1 Answer

  1. Editorial Team

    can you show your markup with the panel and the codebehind where you hide it?

    there’s a difference between setting the Visible property to false and setting the style display attribute to none- the first will not render the element at all, meaning there isn’t anything rendered with the id you’re looking for.

    edit: it’s probably because of the way you’re calling HideControl in the timeout- this should be a function instead of a string.

    try doing 

    function ToggleAlert(_c) {
    setTimeout( 
        function () { 
            HideControl(_c); 
        }, 3000);
}

    just for clarity, when you pass a string to setTimeout, it’s evaluated and then run. the code chunk that eval produces will run in a different scope than your ToggleAlert method, and so _c won’t be available at that time.

    edit: you also need to actually get a reference to the control. you’re passing the id string to ToggleAlert, which relays it to HideControl, which is expecting an object not a string.

    function HideControl(_c) { // _c is the id of the element
    var control = document.getElementById(_c);
    if (control != null)
        control.style.display = 'none';
}
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