jquery中ajax返回值,JQUERY里AJAX返回值的问题

Code Snippet

function useridvalidate()

{

var id=$("#txt_id").val();

if(validate("^[\\w-]{4,20}$",id,false,"#mesg_id","

4-20位由英文、数字及“_”、“-”组成ID
","
请填写用户ID!
"))

{

var mesgcontrol = $("#mesg_id");

mesgcontrol.empty();

mesgcontrol.html("

正在验证用户名，请稍候。。。。。");

var cansub;

mesgcontrol.ajaxStop(

function()

{

return cansub;

}

);

$.get(

"../AjaxResponse/Validate_HasUserId.ashx",

{userid:id},

function(mesg)

{

if("True"==mesg)

{

mesgcontrol.empty();

cansub = true;

}

else

{

mesgcontrol.empty();

mesgcontrol.html("

该用户名已被使用
");

cansub = false;

}

}

);        }

else

{

return false;

}

}

function sub()

{

var b = useridvalidate();

alert(b);

}