Question

 <div id="notifydaydiv" name="notifydaydiv" style="display:none; padding-left:50px">
 <input name="notifyday" type="checkbox" value="wed" /> Wednesday <br />
 <input name="notifyday" type="checkbox" value="thu" /> Thursday <br />
 <span style="color:red; font-size:7pt;">Recommended</span><br />
 <input name="notifyday" type="checkbox" value="fri" checked="checked"/> Friday 
 <div id="day_err"></div>
 <script>
  [ set which checkbox is checked based on the value attr ]
 </script>
</div>

Answer 1

You can find and check it using the attribute-equals selector, like this:

$(":checkbox[value='wed']").attr('checked', true);

You can also use name in there if needed, like this:

$(":checkbox[name='notifyday'][value='wed']").attr('checked', true);