<div class="a" onclick="doA();">
  <span class="b" onclick="doB(event);">BBBB</span>
AAAA
</div>
<script>
function doA(){
    alert("a")
}
function doB(evt){
    alert("b");
    var evt = evt;
    window.event?evt.cancelBubble=true:evt.stopPropagation();
}
</script>

------解决方案--------------------

HTML code

<div class="a" onclick="doA();">
  <span class="b" onclick="doB('ok', event);">BBBB</span>
AAAA
</div>
<script>
function doA(){
    alert("a")
}
function doB(s, evt){
    alert(s);
    var evt = evt;
    window.event?evt.cancelBubble=true:evt.stopPropagation();
}

</script>