<script>
  function selectAll(name, select) {
    var oObject = document.all.item(name);
    if (oObject != null){
      if (oObject.length != null){
        for (i = 0; i < oObject.length; i++){
          oObject(i).checked = select;
        }
      } else {
        oObject(i).checked = select;
      }
    }
  }
</script>

<script>
  function selectAll(f, select) {
    if (f != null && f.elements.length != 0){
        for (i = 0; i < f.elements.length; i++){
          if(f.elements .type == 'checkbox') {
            f.elements.checked = true;
          } 
        }
     }
  }
</script>

<form>
<input type="checkbox" onclick="selectAll(this.form);"/>