How to call code behind method from a javascript function?

How to call code behind method from a javascript function?

I am having an javascript function for a HTML img click event in aspx
page. And a server Method in its code behind page.Now I want to call the
server method from the javascript function without any parameter only when
the HTML img is clicked by the user.
C# Code Behind Method:
[WebMethod]
public void PopUpClick(object sender, EventArgs e)
{
//Something;
}
JavaScriptMethod:
$(document).ready(function () {
$('.clickme').click(function () {
PageMethods.PopUpClick();
});
});
Also I added into the master page: <asp:ScriptManager ID="ScriptManager1"
runat="server" EnablePartialRendering="true" EnablePageMethods="true" />
It is not working.When I debugging this Javascript function on the Chrome
I saw an error:Uncaught Reference Error:PageMethods is not defined.
Can anyone help me on this ?. Thanks in advance.