请使用JS-SDK的 FB.getLoginStatus（）方法：

Make use of the JS-SDK FB.getLoginStatus() method:

FB.getLoginStatus(function(response) {
  if (response.authResponse) {
    // logged in and connected user, someone you know
    // reload page or use ajax to update content of page
  } else {
    // no user session available, someone you dont know
  }
});