Microsoft JScript运行时错误:“RequestCompleted”未定义

运行以下代码时会出现上述错误:

    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(RequestCompleted);

在此区块内:

<script language="javascript" type="text/javascript">
    var postBackElement;

    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(RequestCompleted);
    Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(InitializeRequestHandler);

    function InitializeRequestHandler(sender, args) {
        //set the postBackElement
        postBackElement = args.get_postBackElement();
    }