js/stack.js

(function () {
  const stackedCardsSection = document.getElementById("stacked-cards-section");
  const stickyHeader = stackedCardsSection.children[0];
  const stackedCards = document.getElementById("stacked-cards");
  const cardsArray = Array.from(stackedCards.children);
  const cardsHeights = cardsArray.map(
    (card) => card.children.item(0).getBoundingClientRect().height
  );

  const mobileAndTabletCheck = function () {
    let check = false;
    (function (a) {
      if (
        /(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino|android|ipad|playbook|silk/i.test(
          a
        ) ||
        /1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test(
          a.substr(0, 4)
        )
      )
        check = true;
    })(navigator.userAgent || navigator.vendor || window.opera);
    return check;
  };

  if (mobileAndTabletCheck() || window.innerWidth < 1024) {
    stackedCards.style.gap = "var(--cardMargin)";
    cardsArray.forEach((card) => (card.style.position = "relative"));
    stickyHeader.style.position = "relative";
    return;
  }

  const percentageSeen = (element, offset) => {
    // Get the relevant measurements and positions
    const viewportHeight = window.innerHeight;
    const scrollTop = window.scrollY;
    const elementOffsetTop = element.offsetTop;
    const elementHeight = element.offsetHeight;

    // Calculate percentage of the element that's been seen
    const distance = scrollTop + viewportHeight - elementOffsetTop - offset;
    const percentage = Math.round(
      distance / ((viewportHeight + elementHeight) / 100)
    );

    // Restrict the range to between 0 and 100
    return Math.min(100, Math.max(0, percentage));
  };

  cardsArray.forEach((card) => {
    card.style.top = `calc(${
      stickyHeader.getBoundingClientRect().height + "px"
    } + var(--cardsSectionGap) + calc(var(--index) * var(--cardTopPadding)))`;
  });

  const headerBottomStop = +getComputedStyle(stackedCardsSection)
    .getPropertyValue("--cardsHeaderBottomStop")
    .slice(0, -2);

  document.addEventListener("scroll", function () {
    const percentageOfSecondCardSeen = percentageSeen(
      cardsArray[1],
      64 + stackedCardsSection.offsetTop
    );
    const percentageOfThirdCardSeen = percentageSeen(
      cardsArray[2],
      128 + stackedCardsSection.offsetTop
    );

    if (
      Math.abs(
        stickyHeader.getBoundingClientRect().bottom -
          stackedCardsSection.getBoundingClientRect().bottom
      ) <
      headerBottomStop + cardsHeights[2]
    ) {
      stickyHeader.children.item(
        0
      ).style.paddingBottom = `calc(var(--cardsHeaderBottomStop) + ${
        cardsHeights[2] + "px"
      })`;
    } else {
      stickyHeader.children.item(0).style.paddingBottom = "";
    }

    cardsArray[0].children.item(0).style.scale =
      1 -
      (0.1 * percentageOfSecondCardSeen) / 100 -
      (0.1 * percentageOfThirdCardSeen) / 100;
    cardsArray[0].children.item(0).style.opacity =
      1 -
      (0.1 * percentageOfSecondCardSeen) / 100 -
      (0.1 * percentageOfThirdCardSeen) / 100;
    cardsArray[0].children.item(0).style.filter = `blur(${
      (10 * Math.max(percentageOfSecondCardSeen - 0.2, 0)) / 100 +
      (10 * Math.max(percentageOfThirdCardSeen - 0.2, 0)) / 100
    }px)`;
    cardsArray[0].style.paddingBottom = `calc(
      var(--cardTopPadding) * 2 - ${cardsHeights[0] - cardsHeights[2]}px
    )`;

    cardsArray[1].children.item(0).style.scale =
      1 - (0.1 * percentageOfThirdCardSeen) / 100;
    cardsArray[1].children.item(0).style.opacity =
      1 - (0.1 * percentageOfThirdCardSeen) / 100;
    cardsArray[1].children.item(0).style.filter = `blur(${
      (10 * Math.max(percentageOfThirdCardSeen - 0.2, 0)) / 100
    }px)`;
    cardsArray[1].style.paddingBottom = `calc(
      var(--cardTopPadding) - ${cardsHeights[1] - cardsHeights[2]}px
    )`;
  });
})();