ext 获取json对象的key跟value

ext 获取json对象的key和value
var json = {"p_AFTER_VALUE":"p", "p_USER_ID:admin", "p_OPER_TIME":"2011-1-19"};

var key ='';
var value ='';
for(var i in json) {
key +=i+",";
value += json[i]+",";
}
alert('key='+key+'      value='+value);