Here is a complete solution

Entire form tag of the asp.net page

<form id="form1" runat="server">    <asp:LinkButton ID="LinkButton1" runat="server" /> <%-- included to force __doPostBack javascript function to be rendered --%>    <input type="button" id="Button45" name="Button45" onclick="javascript:__doPostBack('ButtonA','')" value="clicking this will run ButtonA.Click Event Handler" /><br /><br />    <input type="button" id="Button46" name="Button46" onclick="javascript:__doPostBack('ButtonB','')" value="clicking this will run ButtonB.Click Event Handler" /><br /><br />    <asp:Button runat="server" ID="ButtonA" ClientIDMode="Static" Text="ButtonA" /><br /><br />    <asp:Button runat="server" ID="ButtonB" ClientIDMode="Static" Text="ButtonB" /></form>

Entire Contents of the Page's Code-Behind Class

Private Sub ButtonA_Click(sender As Object, e As System.EventArgs) Handles ButtonA.Click    Response.Write("You ran the ButtonA click event")End SubPrivate Sub ButtonB_Click(sender As Object, e As System.EventArgs) Handles ButtonB.Click    Response.Write("You ran the ButtonB click event")End Sub

• The LinkButton is included to ensure that the __doPostBack javascript function is rendered to the client. Simply having Button controls will not cause this __doPostBack function to be rendered. This function will be rendered by virtue of having a variety of controls on most ASP.NET pages, so an empty link button is typically not needed

What's going on?

Two input controls are rendered to the client:

<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" /><input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />

• __EVENTTARGET receives argument 1 of __doPostBack
• __EVENTARGUMENT receives argument 2 of __doPostBack

The __doPostBack function is rendered out like this:

function __doPostBack(eventTarget, eventArgument) {    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {        theForm.__EVENTTARGET.value = eventTarget;        theForm.__EVENTARGUMENT.value = eventArgument;        theForm.submit();    }}

• As you can see, it assigns the values to the hidden inputs.

When the form submits / postback occurs:

• If you provided the UniqueID of the Server-Control Button whose button-click-handler you want to run (javascript:__doPostBack('ButtonB',''), then the button click handler for that button will be run.

What if I don't want to run a click handler, but want to do something else instead?

You can pass whatever you want as arguments to __doPostBack

You can then analyze the hidden input values and run specific code accordingly:

If Request.Form("__EVENTTARGET") = "DoSomethingElse" Then    Response.Write("Do Something else") End If

Other Notes

• What if I don't know the ID of the control whose click handler I want to run?
  • If it is not acceptable to set ClientIDMode="Static", then you can do something like this: __doPostBack('<%= myclientid.UniqueID %>', '').
  • Or: __doPostBack('<%= MYBUTTON.UniqueID %>','')
  • This will inject the unique id of the control into the javascript, should you wish it

Per Phairoh: Use this in the Page/Component just in case the panel name changes

<script type="text/javascript">     <!--     //must be global to be called by ExternalInterface         function JSFunction() {             __doPostBack('<%= myUpdatePanel.ClientID  %>', '');         }     -->     </script>

While Phairoh's solution seems theoretically sound, I have also found another solution to this problem. By passing the UpdatePanels id as a paramater (event target) for the doPostBack function the update panel will post back but not the entire page.

__doPostBack('myUpdatePanelId','')

*note: second parameter is for addition event args

hope this helps someone!

EDIT: so it seems this same piece of advice was given above as i was typing :)