It's recommended that use both the HTML
target attribute
and an onclick handler to pop the JavaScript window, just on the off chance that the visitor has JavaScript disabled in their browser. In that case, the default HTML behavior will still work.
PHP Code:
<a href="some_page.html" target="popupWin" onclick="window.open('some_page.html','popupWin','width=300,height=400');">Open page in new window</a>