JS with

<script type="text/javascript">
    function Dog(){
        this.type="dog";
        this.tail=1;
        this.bark="wangwang";
    }
    var ahuang=new Dog();
    //alert(ahuang.bark);
    with(ahuang){
        alert(bark);
    }
</script>

with用于引用某js对象的已有属性