首先定义一个json数组对象如下：
var persons = [{name: "tina", age: 14},{name: "timo", age: 15},{name: "lily", age: 16},{name: "lucy", age: 16}
]往数组中添加一个对象：
persons.push({name: "similar", age: 18});判断某个HTML标签是否存在某个属性：
if (typeof(val) == "undefined") {layer.tips("#li_" + id, "请设置值!");return;
}