var ref = "";
if (document.referrer.length > 0) {
ref = document.referrer;
}
if (ref.length == 0 && opener.location.href.length > 0) {
ref = opener.location.href;
}
alert(ref)
More detailed document.referrer compatibility please refer to:
https://blog.csdn.net/flyingpig2016/article/details/53130912