Open popup window using JavaScript

if we want to open a popup window using javascript we can do it by using following function:
javascript:showWindow('mypage.aspx"',800,600,50)

How to use it?

if you want to open popup window using Anchor tag of Html:
< a href='javascript:showWindow('mypage.aspx"',800,600,50)' >click me< /a >

open popup window using Html Button:

< input type="button" id="btnmap" name="btnmap" value="Map" onclick ='javascript:showWindow(< %# """MapDSHotelDetail.aspx?hotelname=" &container.dataitem("hotelname")& "&cityid=" & container.dataitem("cityid") & "&countryid=" & ddlcountry.selectedvalue &"""" % >,800,600)'/ >