How to check for postback using javascript?

Hi,
Is there a way to check for postback in Javascript, just like in ASP.NET that uses the page_load events (see below)?

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
 
           If Not Page.IsPostBack Then
                'DO something here, if page is not postback
           End If
End Sub

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