跨域

server (http://www.b.com/IP.aspx)

protected void Page_Load(object sender, EventArgs e)

{ 

    string callback = Request.QueryString["callback"];

    //testCallback({ip:'192.168.1.1'})

    Response.Write(string.Format("{0}({{ip:'{1}'}})", callback, "192.168.1.1"));

}

client (http://www.a.com/test.aspx);

$(function(){

    $.getJSON('http://www.b.com/IP.aspx?callback=?',function(data){

        alert(data.ip);

    });

});