如何更改滚动位置？

Question

I want to have my content fade in on scrolling, but it reacts to late. How can I change it, to have my content fade in earlier?

I am very new to javascript and couldn't get it worked yet.

$(window).on("load",function() {
  $(window).scroll(function() {
    var windowBottom = $(this).scrollTop() + $(this).innerHeight();
    $(".fade").each(function() {
      /* Check the location of each desired element */
      var objectBottom = $(this).offset().top + $(this).outerHeight();

      /* If the element is completely within bounds of the window, fade it in */
      if (objectBottom < windowBottom) { //object comes into view (scrolling down)
        if ($(this).css("opacity")==0) {$(this).fadeTo(500,1);}
      } else { //object goes out of view (scrolling up)
        if ($(this).css("opacity")==1) {$(this).fadeTo(500,0);}
      }
    });
  }).scroll(); //invoke scroll-handler on page-load
});

Right now the content space is blank until I scroll to the bottom. I need to have my content fade in when it is on like half of the page or earlier. Maybe changeable to any height with percent or pixel?

Answer 1

The shared portion of code fades element in once they are completely in the viewport (= when bottom of the elements is in the window).

How about fading elements in as soon as their tops get in the viewport?

Fade out logic should remain as is: elements should be faded out once their bottom get out of the viewport.

Adapted code:

$(window).on("load",function() {
  $(window).scroll(function() {
    var windowBottom = $(this).scrollTop() + $(this).innerHeight();
    $(".fade").each(function() {
      /* Check the location of each desired element */
      var objectTop = $(this).offset().top
          , objectBottom = $(this).offset().top + $(this).outerHeight();

      /* If the element's top gets within bounds of the window, fade it in */
      if (objectTop < windowBottom) { //object comes into view (scrolling down)
        if ($(this).css("opacity")==0) {$(this).fadeTo(500,1);}
      } else if (objectBottom >= windowBottom){ //object goes out of view (scrolling up)
        if ($(this).css("opacity")==1) {$(this).fadeTo(500,0);}
      }
    });
  }).scroll(); //invoke scroll-handler on page-load
});