用字面量创建对象桌子，有属性：长、宽、高、面积、体积 有方法：求面积、求体积

<script>
    var table = {
        length: 60,
        width: 40,
        height: 120,
        getArea : function () {
            var area= this.length * this.width;
            var volume = this.length* this.width*this.height
            document.write("面积："+area);
            document.write('<br>'+"体积："+volume);
            return area;
        }
    }
    table.getArea();
</script>