<style>
span{border:1px solid red;padding:0 30px}
</style>
</head>
<body>
<div id="tar">
<span class="navigatorItem" id="id_0"></span>
<span class="navigatorItem" id="id_1"></span>
<span class="navigatorItem" id="id_2"></span>
</div>
<script>
document.getElementById('tar').onclick=function fn(e){
e = e || event
var target = e.target || e.srcElement
alert('click:'+target.id)
}
</script>
http://learn.javascript.ru/bubbling-and-capturing