js 把对象转为json字符串

function obj2str(o){
    var r = [];
    if(typeof o =="string") return "\""+o.replace(/([\'\"\\])/g,"\\$1").replace(/(\n)/g,"\\n").replace(/(\r)/g,"\\r").replace(/(\t)/g,"\\t")+"\"";
    if(typeof o =="undefined") return "undefined";
    if(typeof o == "object"){
        if(o===null) return "null";
    else if(!o.sort){
            for(var i in o)
                r.push("\""+i+"\""+":"+obj2str(o[i]))
            r="{"+r.join()+"}"
        }else{
            for(var i =0;i<o.length;i++)
                r.push(obj2str(o[i]))
            r="["+r.join()+"]"
        }
        return r;
    }
    return o.toString();
}


var cmt = new Object;
var jsonstr= '';

  cmt.username  = $("#username").value();
  cmt.email         =  $("#email").value();
  cmt.content      = $("#content").value();

jsonstr =  obj2str(cmt );