How to Check Async postback in Asp.net triggerd by update panel

Kindly Check the below condition to know whether its a synchronous postback or Asynchronous postback

var scriptManager = ScriptManager.GetCurrent(this.Page);

if (scriptManager != null && scriptManager.IsInAsyncPostBack)

ScriptManager.RegisterStartupScript(this, this.GetType(), "temp", "<script  language='javascript'>Init();</script>", false);