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Asked: 2026-05-22T15:32:05+00:00

I have a fixed-position image that I would like to fade out when scrolling

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I have a fixed-position image that I would like to fade out when scrolling the page. I’ve written a rather basic jQuery script to do so, and I imagine it is not the most efficient because it is polling constantly on page scrolling. I was wondering if there is a more efficient way to achieve what I am trying to do?

As I have it coded now, my browser is using basically 40-50% CPU when viewing the page.

Currently I have it working as so: http://jsbin.com/iwiqe4/2

JS:

$(document).ready(function(){
  $(window).scroll(function(){
      if (1-$(window).scrollTop()/200 > -10) {
          $("#icon").css({opacity: 1-$(window).scrollTop()/200});
      }
    });
});

HTML:

<!DOCTYPE html>
<html>
<head>
<script class="jsbin" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<meta charset=utf-8 />
<title>JS Bin</title>
<!--[if IE]>
  <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<style>
  article, aside, figure, footer, header, hgroup, 
  menu, nav, section { display: block; }

  body {
    width: 400px;
    margin: 0 auto;
  }

  #icon {
    position: fixed;
    top: 50px;
    left: 50%;
    margin-left: -200px;
    z-index: 1;
  }

  #text {
    margin-top: 300px;
    z-index: 50;
    position: relative;
  }
</style>
</head>
<body>
  <div id="icon"><img src="http://placehold.it/400x200" /></div>

  <div id="text">
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p>
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p>
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p>
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p>
  <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p>
  </div>
</body>
</html>
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1 Answer

  1. Editorial Team

    You are absolutely correct in thinking that calling that function on window scroll is where the performance problems lie. Here’s an excellent article by John Resig that talks about a similar problem that Twitter had.

    As @Guy says, you’ll want to use setInterval and check the scroll state. Also make sure to cache your queries like John mentions in the article (shamelessly adapted from John’s code at the bottom of the article):

    $(document).ready(function(){
  var didScroll = false;
  var icon = $("#icon");
  var $window = $(window);

  $(window).scroll(function(){
      didScroll = true;
  });

  window.setInterval(function () {
    if (didScroll) {
      if (1-$window.scrollTop()/200 > -10) {
          icon.css({opacity: 1-$window.scrollTop()/200});
      }
      didScroll = false;
    }
  }, 50);
});

    http://jsbin.com/iwiqe4/6/

    I would adjust the interval to be the highest value that still looks good (50 looked fine on my machine). I’ve also cached all of the queries that were inside of the event handler. Querying the DOM is expensive, and doing it on every page scroll could cause problems quickly.

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