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javascript - How to make a sidebar sticky when scrolling between header and footer with jQuery (without scrolling over them)?

I need a strictly jQuery solution for this problem. This is because I'm using Wordpress and the sidebar widget that I want to make sticky is inside an <aside> element which I cannot make full height.

In the same way that .scrollTop() detects how far down the page I am to make the sidebar widget sticky I need JS detect how far up I am from the bottom of the page to "unstick" the widget via assigning a new fixed position.

I tried to to this with .offset() but I have been unable to make it work so far.

  function stopDiv() {
    var distance = $('.footer').offset().top - $('.widget').offset().top;
    if (distance < 10) {
      $('.widget').css({
        'top': 'auto',
        'bottom': '10px'
      });
    }
  }

As you can see in the snippet below my sidebar scrolls as it should, but I want the sidebar to assume a new fixed position when I reach <10px distance from the footer.

I want the sidebar to assume a new fixed position above the footer until the user scrolls back up.

Edit: The solution suggested below by @Benvc works fine in the snippet, but not on my wordpress site. Here are the console errors I'm getting:

scripts.js:18 Uncaught ReferenceError: s is not defined
    at HTMLDocument.<anonymous> (scripts.js:18)
    at i (jquery.js:2)
    at Object.fireWith [as resolveWith] (jquery.js:2)
    at Function.ready (jquery.js:2)
    at HTMLDocument.K (jquery.js:2)
    at HTMLDocument.s (VM11874 rocket-loader.min.js:1)
    at p (VM11874 rocket-loader.min.js:1)
    at t.simulateStateAfterDeferScriptsActivation (VM11874 rocket-loader.min.js:1)
    at Object.callback (VM11874 rocket-loader.min.js:1)
    at t.run (VM11874 rocket-loader.min.js:1)

  // Fixed Widget
  function fixDiv() {
    var $cache = $('.widget');
    if ($(window).scrollTop() > 380)
      $cache.css({
        'position': 'fixed',
        'top': '10px',
        'right': '30px'
      });
    else
      $cache.css({
        'position': 'relative',
        'top': 'auto',
        'right': 'auto'
      });
  }
  $(window).scroll(fixDiv);
  fixDiv();

/* My attempt 
  function stopDiv() {
    var distance = $('.footer').offset().top - $('.widget').offset().top;
    if (distance < 10) {
      $('.widget').css({
        'top': 'auto',
        'bottom': '10px'
      });
    }
  }
  $(window).scroll(stopDiv);
  stopDiv();
  */
@import url('https://fonts.googleapis.com/css?family=Open+Sans:400,700');
* {
  font-family: 'Open Sans';
  color: #fff;
  box-sizing: content-box;
}

body {
  padding: 0;
  margin: 0;
}

p {
  margin: 20px;
}

hr {
  width: 85%;
  border-style: solid;
}

.main-content {
  width: 100%;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: 150px auto;
  grid-template-areas: "nav nav nav nav" "main main main sidebar";
  grid-column-gap: 20px;
  grid-row-gap: 0px;
}

.nav {
  grid-area: nav;
  background-color: #266392;
  display: grid;
  grid-template-columns: 1fr 3fr 1fr;
}

.nav h1 {
  place-self: center;
  font-weight: 400;
  font-size: 40px;
  grid-column: 2;
}

.nav i {
  align-self: center;
  font-size: 40px;
}

.main {
  height: 1500px;
  width: 98%;
  justify-self: start;
  grid-area: main;
  padding: 10px;
  float: left;
  background-color: #e8624c;
  margin: 10px;
}

.sidebar-container {
  height: 900px;
  width: 300px;
  justify-self: start;
  background-color: #209B66;
  grid-area: sidebar;
  grid-column: 4;
  top: 10px;
  margin: 10px;
  padding: 20px;
  display: grid;
  grid-template-rows: auto;
  grid-row-gap: 10px;
}

.sidebar-container>p {
  display: grid;
  align-items: start;
  padding: 0;
  margin: 0;
}

.widget {
  height: 500px;
  width: 300px;
  background-color: #E3962F;
}

.footer {
  background-color: #333;
  height: 800px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<body>
  <div class="main-content">
    <div class="nav">
      <h1>Sticky Sidebar Problem</h1>
      <i class="fa fa-arrow-down" aria-hidden="true"></i>
    </div>
    <div class="main">
      <p>
        [Main Content]
      </p>

    </div>
    <div class="sidebar-container">
      <p>[Sidebar Container]</p>

      <div class="widget">
        <p> [Widget]</p>
      </div>
    </div>
  </div>
  <div class="footer"></div>
</body>
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1 Answer

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by (71.8m points)

We can break this up into 2 different problems. Problem #1, you need the bottom Y-chord of your element (a), and Problem #2 you need the bottom of the page (b). If you have this data, then your answer is simply (b - a).

To help us, let's create a helper function as such:

function getOffset(el) {
  const rect = el.getBoundingClientRect();
  return {
    left: rect.left + window.scrollX,
    right: rect.left - window.scrollX,
    top: rect.top + window.scrollY,
    bottom: rect.bottom -window.scrollY
  };
}

Using this, it should be as simple as getOffset(document.body).bottom - getOffset(yourElement).bottom.

Hope this helps!

(Note that I can't actually test this code now so it may not work out of the box, so use it more as a guide not a copy/paste).


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