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The OnRequestStart client-side event handler is called when a request to the server is started. The event can be initially triggered by an initiating control configured in RadAjaxManager settings, a control within a RadAjaxPanel or by a client-side ajaxRequest() call. The event can be cancelled.

Two parameters are passed to the event handler with the following methods:

  • sender - The instance of the client-side RadAjaxManager /RadAjaxPanel object.

  • eventArgs , which has the following methods:

  • set_cancel() - Lets you permit or block the AJAX request from continuing. Calling set_cancel(true) prevents the request from continuing.

  • get_eventTarget() - Gets the UniqueID of the element that had raised the request.

  • get_eventArgument() - Gets the string passed in the initial AJAX request.

  • get_eventTargetElement() - Gets the instance of the client-side object that raised the AJAX request. You can iterate each of the settings and retrieve the initiating control id and another array of objects that represent updated controls.

  • get_enableAjax() , set_enableAjax() - Gets or sets if an AJAX request is performed. set_enableAjax(false) causes the request to be performed via standard postback.

The example below displays the control that initiated the request.

<script type="text/javascript">
    function requestStart(sender, eventArgs) {
        alert('Request start');
<telerik:RadAjaxPanel ID="RadAjaxPanel1" runat="server" ClientEvents-OnRequestStart="requestStart">
    <telerik:RadButton RenderMode="Lightweight" runat="server" Text="Click me!"></telerik:RadButton>

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