Javascript “推荐人”页面不显示

虽然我是从主页进入表单页面的，但是推荐人页面没有出现。我怎样才能解决这个问题

document.referrer == ""

许多网站重定向到example.com/thank-you页面，所以我想获得引用它的页面

example.com/form redirects to example.com/thank-you
example.com/form1 redirects to example.com/thank-you
example.com/form2 redirects to example.com/thank-you
example.com/form3 redirects to example.com/thank-you
example.com/form4 redirects to example.com/thank-you
example.com/form5 redirects to example.com/thank-you