jquery和json使用代码

本人经常用的代码

$.ajax(
    {
    type: "post",
    url: "<%=request.getContextPath()%>/msg.do",
    datatype:"json",
    data:str,
    success:function(msg){
    if(msg!=null &&msg!="" && msg!="[null]" && msg!="null")
    {
     var msgobj=eval(msg);
     var tipmessage="";
     for(var i=0;i<msgobj.length;i++)
     {
      var obj=msgobj[i];
      ctx.innerHTML=ctx.innerHTML+"<div id="+obj.id+">"+obj.sendUser+"&nbsp;"+obj.sendTimeStr+"<br/>&nbsp;&nbsp;&nbsp;&nbsp;"+obj.content+"</div><p/>"
      tipmessage=tipmessage+obj.sendUser+"发送一条消息<br/>";
     }
     if(msgobj.length>0){
      tipyou(tipmessage);
      window.focus();
      }
    }
    }});