参考 mozilla文档
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON
用来把json字符串解析成json对象
var classInfo = '{\"LiMing\": {\"age\": 23, \"gender\": \"male\"}, \"XiaoHong\": {\"age\": 24, \"gender\": \"female\"}}';
var obj = JSON.parse(classInfo);
alert(obj);