js实现ifram取父窗口URL地址的方法

var url='';
try { 
    url = window..document.referrer ; 
} catch(M) { 
    if (window.parent) { 
      try { 
        url = window.parent.document.referrer;
      } catch(L) { 
        url = "";
      } 
    } 
} 
if (url === "") { 
    url = document.referrer;
}