是否可以使用javascript打开弹出窗口并运行一次

Question

Is it possible (and how?) to make it only run, once, that the function does not continue to be executed once closed

;(function($){
    $(window).scroll(function(){
    if($(document).scrollTop()>=$(document).height()/5)
        $("#xpopup").show("slow");else $("xpopup").hide("slow");

});

})(jQuery);

function closePopup(){
    jQuery('#xpopup').hide('slow');
}

HTML

<div id="xpopup" style="display: none;">
    <a style="position:absolute;top:14px;right:10px;color:#999;font-size:20px;font-weight:bold;" href="javascript:void(0);" onclick="return closePopup();">
        <img src="close.png" width="18" height="18"/>
    </a>
    popup content
</div>

Answer 1

After displaying the popup, remove the scroll handler with .off() :

if($(document).scrollTop() >= $(document).height() / 5) {
    $("#xpopup").show("slow");
    $(window).off('scroll');
}

Note that this will remove all scroll handlers from the window. If you only have one, that's not a problem. If you have more, store a reference to this scroll handler and pass it to .off() :

$(window).off('scroll', myScrollPopupHandler);

Answer 2

I would use singleton

function singleton(){
    let instance;

  let createInstance = function(){
    return 'I exist';  //replace with actual object (e.g. your instance that would cause the alert)

  }

  return {
    createAlert : function(){
        if(!instance){
        instance = createInstance();
        alert(instance);
      }
    }
  }
}();

singleton.createAlert(); //this would go into your desired event

The reason why this might be a good way to do it is that you would likely replace alert with some other action. In that case all you need to do is to replace instance with whatever object that may cause the invokation (eg bootstrap alert).