Adding animation between adding and removing two classes

Question

I am working on the demo below. Why am I not able to generate smooth transition (something like Smooth Scroll) between adding and removing two classes fixed-top and fixed-bottom while I already added following css roles into them?

  -webkit-transition: all 3s ease;
  -moz-transition: all 3s ease;
  -o-transition: all 3s ease;
  transition: all 3s ease;

var lastScrollTop = 0;
$(window).scroll(function(event) {
  var st = $(this).scrollTop();
  if (st > lastScrollTop) {
    if (st > 500) {
      $('.box').removeClass("fixed-bottom").addClass("fixed-top");
    }
  } else {
    if (st < 500) {
      $('.box').removeClass("fixed-top").addClass("fixed-bottom");
    }
  }
  lastScrollTop = st;
});

html,
body {
  height: 100%;
}

.container {
  height: 2000px;
}

.box {
  width: 100%;
  height: 50px;
  background: #777;
}

.fixed-top {
  position: fixed;
  top: 0;
  -webkit-transition: all 3s ease;
  -moz-transition: all 3s ease;
  -o-transition: all 3s ease;
  transition: all 3s ease;
}

.fixed-bottom {
  position: fixed;
  bottom: 0;
  -webkit-transition: all 3s ease;
  -moz-transition: all 3s ease;
  -o-transition: all 3s ease;
  transition: all 3s ease;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="container">
  <div class="box fixed-bottom"></div>
</div>

What is the best way to do this (having smooth moving up and down)?

Banzay · Accepted Answer · 2016-11-23 20:00:53Z

1

A stripe jumps up and down because you didn't set values of bottom within .fixed-top and top within .fixed-bottom, then transition prosessor can't realize wich attribute to transite. You need to get window.height() to transite properly. You can do it using jquery, wich makes your css shorter Look at snippet

var lastScrollTop = 0;
var y = $( window ).height() - $('.box').height() + "px";
$('.box').css("top", y);
$(window).scroll(function(event) {
  var st = $(this).scrollTop();
  if (st > lastScrollTop) {
    if (st > 500) {
      $('.box').css("bottom", y);
      $('.box').css("top","0");
    }
  } else {
    if (st < 500) {
      $('.box').css("top", y);
      $('.box').css("bottom","0");
    }
  }
  lastScrollTop = st;
});

html,
body {
  height: 100%;
}

.container {
  height: 2000px;
}

.box {
  width: 100%;
  height: 50px;
  position: fixed;
  bottom: 0;
  background: #777;
  -webkit-transition: all 3s ease;
  -moz-transition: all 3s ease;
  -o-transition: all 3s ease;
  transition: all 3s ease;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="container">
  <div class="box fixed-bottom"></div>
</div>

answered Nov 23, 2016 at 20:00

Banzay

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1 Comment

user1760110 Over a year ago

Thanks a lot Banzay

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