<input type="button" onclick="aa()" ondblclick="bb()" value="点我">
<script language="javascript">
var isdb;
function aa(){
    isdb=false;
    window.setTimeout(cc, 500)
    function cc(){
        if(isdb!=false)return;
        alert("这是单击")
    }
}
function bb(){
    isdb=true;
    alert("这是双击")
}
</script>