JS方法里面没有加return，就出错了？

Question

ReadCookie_sns = function(){   ReadCookie("myname"); }出错，提示：Unexpected token u in JSON at position 0改为：ReadCookie_sns = function(){ return  ReadCookie("myname"); }好了。 加了return, 就好了。请问为什么？-----------------下面是ReadCookie方法。ReadCookie = function(cookieName) {        var theCookie = "" + document.cookie;        var ind = theCookie.indexOf(cookieName);        if (ind == -1 || cookieName == "") return "";        var ind1 = theCookie.indexOf(';', ind);        if (ind1 == -1) ind1 = theCookie.length;        /*读取Cookie值*/        return unescape(theCookie.substring(ind + cookieName.length + 1, ind1));    }