进入视口时，仅自动滚动嵌入式窗口一次。 无法向上滚动

Question

I have an image embedded in a container with a background image to give the effect of scrolling within the page. Initially, I had the scrolling effect take place on page load, with this simple bit of script which worked perfectly.

 $(window).on("load", function () {
    $(".embedded_scroller_image").animate({ scrollTop: $('.embedded_scroller_image')[0].scrollHeight}, 2500, "easeInOutCubic");
}); // end on load 

However, the element is too far down the page now and I want that animation to fire when the element enters 80% of the viewport. That part is also working fine with this code here (I'm using a scroll limiter to improve browser performance)

 // limit scroll call for performance
     var scrollHandling = {
      allow: true,
      reallow: function() {
        scrollHandling.allow = true;
      },
    delay: 500 //(milliseconds) adjust to the highest acceptable value
  };

$(window).on('scroll', function() {
  var flag = true;
    if(scrollHandling.allow) { // call scroll limit
        var inViewport = $(window).height()*0.8; // get 80% of viewport
        $('.embedded_scroller_image').each(function() { // check each embedded scroller
            var distance = $(this).offset().top - inViewport; // check when it reaches offset
            if ($(window).scrollTop() >= distance && flag === true ) {
              $(this).animate({ scrollTop: $(this)[0].scrollHeight}, 2500, "easeInOutCubic"); //animate embedded scroller
              flag = false;
            } 
          });
      } // end scroll limit
  }); // end window scroll function

The problem is this: I want the autoscroll to happen once and then stop. Right now, it works on entering viewport, but if I then try to manually scroll the image, it keeps pushing back down or stutters. You can't get the element to scroll normally. I attempted to use the flag in the code to stop the animation, but couldn't get that to successfully work.

How can I have this animation fire when the element is 80% in the viewport, but then completely stop after one time?

Here is a codepen I mocked up as well http://codepen.io/jphogan/pen/PPQwZL?editors=001 If you scroll down, you will see the image element autoscroll when it enters the viewport, but if you try to then scroll that image up in its container, it won't work.

Thanks!

Answer 1

I have tweaked your script a bit:

// limit scroll call for performance
var scrollHandling = {
    allow: true,
    reallow: function() { scrollHandling.allow = true; },
    delay: 500 //(milliseconds) adjust to the highest acceptable value
};

$(window).on('scroll', function() {

if(scrollHandling.allow) { // call scroll limit
    var inViewport = $(window).height()*0.8; // get 80% of viewport

    $('.embedded_scroller_image').each(function() { // check each embedded scroller
        var distance = $(this).offset().top - inViewport; // check when it reaches offset

        if ($(window).scrollTop() >= distance ) {
            $(this).animate({ scrollTop: $(this)[0].scrollHeight}, 2500, "easeInOutCubic"); //animate embedded scroller
            scrollHandling.allow = false;
        } 

    });

} // end scroll limit

}); // end window scroll function

I have kicked out your flag and simply made use of scrollHandling.allow declared already.

Try if it works for you :)

Cheers!