技巧是检查单击的元素是否具有父.responsive-menu或.menu-btn.

The trick is to check if the element clicked has a parent .responsive-menu or .menu-btn.

如果两者都不存在且菜单已展开，请切换！

If it has'n any of the two and the menu is expanded, toggle!

更新了小提琴

$(document).on("click", function(e){
  if( 
    $(e.target).closest(".responsive-menu").length == 0 &&
    $(".responsive-menu").hasClass("expand") &&
    $(e.target).closest(".menu-btn").length == 0
  ){
    $('.responsive-menu').toggleClass('expand');
  }
});