How to prevent redirect after hyperlink click?

You can simply remove the href attribute:

<a id='key' onclick="func(0)">foo</a>

Change it to:

                            vvvvvvv
<a href="#" id=key onclick="return func(0)">foo</a>

Use javascript:void(0); instead of # as follows:

<a href="javascript:void(0);" id=key onclick="func(0)">foo</a>