Hemant Vishwakarma: GSAP: Pin progress bar when it hits element + progress bar not accrate

I'm trying to create a progress bar that shows how much of a certain element the user still has left to view. Here are some details:

.postProgressBar appears by default under .postHeroImage
When the user scrolls, I want the .postProgressBar to slowly fill up based on how much of the .spacer element there is left to scroll to.
When the .postProgressBar hits the bottom of my header, I want it to become fixed to the bottom of the header (and to unfix when .postHeroImage is in view again).

See my current approach:

$(function() {

gsap.registerPlugin(ScrollTrigger);

  $(window).scroll(function() {
    var scroll = $(window).scrollTop();
    if (scroll >= 1) {
      $(".header").addClass("fixed");
    } else {
      $(".header").removeClass("fixed");
    }
  });
  
    var action = gsap.set('.postProgressBar', { position:'fixed', paused:true});

  gsap.to('progress', {
    value: 100,
    ease: 'none',
    scrollTrigger: {
      trigger: "#startProgressBar",
      scrub: 0.3,
      markers:true,
      onEnter: () => action.play(),
      onLeave: () => action.reverse(),
      onLeaveBack: () => action.reverse(),
      onEnterBack: () => action.reverse(),
    }
  });

});

body {
  background-color: lightblue;
  --white: #FFFFFF;
  --grey: #002A54;
  --purple: #5D209F;
}

.header {
  position: absolute;
  top: 0;
  width: 100%;
  padding: 20px 15px;
  z-index: 9999;
  background-color: var(--white);
}
.header.fixed {
  position: fixed;
  background-color: var(--white);
  border-bottom: 1px solid var(--grey);
}

.postHeroImage {
  padding: 134px 0 0 0;
  margin-bottom: 105px;
  position: relative;
}
.postHeroImage__bg {
  background-size: cover;
  background-repeat: no-repeat;
  width: 100%;
  min-height: 400px;
}

progress {
  position: absolute;
  bottom: -15px;
  left: 0;
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 15px;
  border: none;
  background: transparent;
  z-index: 9999;
}

progress::-webkit-progress-bar {
  background: transparent;
}

progress::-webkit-progress-value {
  background: var(--purple);
  background-attachment: fixed;
}

progress::-moz-progress-bar {
  background: var(--purple);
  background-attachment: fixed;
}

.spacer {
  height: 1000vh;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/3.9.0/gsap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/3.9.0/ScrollTrigger.min.js"></script>

<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet">


<body>

  <header class="header">Header</header>

  <section class="postHeroImage" id="startProgressBar">

    <progress class="postProgressBar" max="100" value="0"></progress>

    <div class="container">
      <div class="row">
        <div class="col-12">
          <div class="postHeroImage__bg" style="background-image: url( 'https://picsum.photos/200/300' );" loading="lazy"></div>
        </div>
      </div>
    </div>
  </section>

  <div class="spacer">lorum ipsum</div>

</body>

Current issues:

The .postProgressBar doesn't become fixed (can't see fixed inline style in inspect mode)
The .postProgressBar is showing progress that isn't accurate based on the amount of .spacer there is left to scroll.

from GSAP: Pin progress bar when it hits element + progress bar not accrate

Hemant Vishwakarma

Tuesday 28 December 2021

GSAP: Pin progress bar when it hits element + progress bar not accrate

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