Convert checkall checkbox to checkall button

[MRGTB]

In my hack I'm using a checkall CHECKBBOX to select and unselect other checkboxes boxes (put tick in and out of them). But I want to remove that checkbox and instead use a BUTTON that when clicked, will do the same thing. tick and untick the other checkboxes.



Here is my javascript code to look at how its configured.

function em_size(str) {

 var a = document.getElementsByName(str);

 var n = a.length;

 try {

  var input_checkall = document.getElementById("checkall_"+str);

  var size = 0;

  input_checkall.checked = true ;

  for (var i=0; i < n; i++) {

   if (a[i].checked) {

    var piecesArray = a[i].value.split( "|" );

    size += piecesArray[3]*1;

   } else {

    input_checkall.checked = false;

   }

And here is the checkall/uncheck "checkbox" code I want converting over to a button instead that does the same thing. Checking/unchecking the other checkboxes

<tr align="left" class="alt2"><td width="80%" align="left"><input type="checkbox" id="checkall_ed2k$rand" onclick="checkAll('ed2k$rand',this.checked)" checked="checked" />&nbsp;<label for="checkall_ed2k$rand"></label>Check all - Uncheck all</td>

Anybody got any ideas on converting this, becuase I can't seem to get it to work and I've been trying all day. I could really do with some help on this one.