voucher-itpln/ud-menu-scroll.js

      // ==== for menu scroll
      const pageLink = document.querySelectorAll(".ud-menu-scroll");

      pageLink.forEach((elem) => {
        elem.addEventListener("click", (e) => {
          e.preventDefault();
          document.querySelector(elem.getAttribute("href")).scrollIntoView({
            behavior: "smooth",
            offsetTop: 1 - 60,
          });
        });
      });

      // section menu active
      function onScroll(event) {
        const sections = document.querySelectorAll(".ud-menu-scroll");
        const scrollPos =
          window.pageYOffset ||
          document.documentElement.scrollTop ||
          document.body.scrollTop;

        for (let i = 0; i < sections.length; i++) {
          const currLink = sections[i];
          const val = currLink.getAttribute("href");
          const refElement = document.querySelector(val);
          const scrollTopMinus = scrollPos + 73;
          if (
            refElement.offsetTop <= scrollTopMinus &&
            refElement.offsetTop + refElement.offsetHeight > scrollTopMinus
          ) {
            document
              .querySelector(".ud-menu-scroll")
              .classList.remove("active");
            currLink.classList.add("active");
          } else {
            currLink.classList.remove("active");
          }
        }
      }

      window.document.addEventListener("scroll", onScroll);