var jsondate={"con":[{"name":"hello","sex":"M"},{"name":"world","sex":"W"},{"name":"helloworld"
    ,"age":"20"}],"con1":[{"names":"hello","sex":"M"},{"names":"world","sex":"W"},{"names":"helloworld"
    ,"ages":"12"}]}

alert(jsondate.con[2].name);//con[2]  中括号按照取索引数组的形式来取值,在js中使用(.)点来获取内容
js将字符串转化为json 可以使用eval()函数也可以使用JSON.parse(str)来转换