JQUERY scrolling固定TAB栏

<script src="https://cdn.staticfile.org/jquery/3.2.1/jquery.min.js"></script>

<script> 
class StickyNavigation {
    
    constructor() {
        this.currentId = null;
        this.currentTab = null;
        this.tabContainerHeight = 70;
        let self = this;
        $('.navs').click(function() { 
        self.onTabClick(event, $(this)); 
        });
        $(window).scroll(() => { this.onScroll(); });
        $(window).resize(() => { this.onResize(); });
    }
    
    onTabClick(event, element) {
        event.preventDefault();
        let scrollTop = $(element.attr('href')).offset().top - this.tabContainerHeight + 1;
        $('html, body').animate({ scrollTop: scrollTop }, 600);
    }
    
    onScroll() {
        this.checkTabContainerPosition();
    this.findCurrentTabSelector();
    }
    
    onResize() {
        if(this.currentId) {
        this.setSliderCss();
        }
    }
    
    checkTabContainerPosition() {
        let offset = $('.nav-items').offset().top + $('.nav-items').height() - this.tabContainerHeight;
        if($(window).scrollTop() > offset) {
        $('.items-container').addClass('items-container--top');
        } 
        else {
        $('.items-container').removeClass('items-container--top');
        }
    }
    
    findCurrentTabSelector(element) {
        let newCurrentId;
        let newCurrentTab;
        let self = this;
        $('.navs').each(function() {
        let id = $(this).attr('href');
        let offsetTop = $(id).offset().top - self.tabContainerHeight;
        let offsetBottom = $(id).offset().top + $(id).height() - self.tabContainerHeight;
        if($(window).scrollTop() > offsetTop && $(window).scrollTop() < offsetBottom) {
        newCurrentId = id;
        newCurrentTab = $(this);
        }
        });
        if(this.currentId != newCurrentId || this.currentId === null) {
        this.currentId = newCurrentId;
        this.currentTab = newCurrentTab;
        this.setSliderCss();
        }
    }
    
    setSliderCss() {
        let width = 0;
        let left = 0;
        if(this.currentTab) {
        width = this.currentTab.css('width');
        left = this.currentTab.offset().left;
        }
        $('.bottom-slider').css('width', width);
        $('.bottom-slider').css('left', left);
    }
    
}
new StickyNavigation();
</script>

---

HTML:

<section class="nav-items">
    <h1>STICKY NAVIGATION BAR</h1>
    <h3>Sticky Nav With Sliding Nav</h3>
    <div class="items-container">
      <a class="navs" href="#sec-html">HTML</a>
      <a class="navs" href="#sec-css">CSS</a>
      <a class="navs" href="#sec-js">JavaScript</a>
      <a class="navs" href="#sec-php">PHP</a>
      <a class="navs" href="#sec-sql">MySQL</a>
      <span class="bottom-slider"></span>
    </div>
  </section>
 
 
  <main class="content">
    <section class="bottom-slide" id="sec-html">
      <h1>HTML</h1>
      <h3>topics about HTML</h3>
    </section>
    <section class="bottom-slide" id="sec-css">
      <h1>CSS</h1>
      <h3>topics about CSS</h3>
    </section>
    <section class="bottom-slide" id="sec-js">
      <h1>JavaScript</h1>
      <h3>topics about JavaScript</h3>
    </section>
    <section class="bottom-slide" id="sec-php">
      <h1>PHP</h1>
      <h3>topics about PHP</h3>
    </section>
    <section class="bottom-slide" id="sec-sql">
      <h1>MySQL</h1>
      <h3>topics about MySQL</h3>
    </section>
  </main>

---

CSS:

  <style>
  body {
  font-family: "Century Gothic", 'Lato', sans-serif;
}
a {
  text-decoration: none;
}
.nav-items,
.bottom-slide {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100vh;
  position: relative;
  background: #eee;
  text-align: center;
  padding: 0 2em;
}
.nav-items h1,
.bottom-slide h1 {
  font-size: 2rem;
  margin: 0;
  letter-spacing: 1rem;
  color: #ff5f14;
}
.nav-items h3,
.bottom-slide h3 {
  font-size: 1rem;
  letter-spacing: 0.3rem;
  opacity: 0.6;
}
.items-container {
  display: flex;
  flex-direction: row;
  position: absolute;
  bottom: 0;
  width: 100%;
  height: 70px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.1);
  background: #fff;
  z-index: 10;
}
.items-container--top {
  position: fixed;
  top: 0;
}
.navs {
  display: flex;
  justify-content: center;
  align-items: center;
  flex: 1;
  color: #212121;
  letter-spacing: 0.1rem;
  transition: all 0.5s ease;
  font-size: 0.8rem;
}
.navs:hover {
  color: white;
  background: rgb(255,95,20, 0.8);
  transition: all 0.5s ease;
}
.bottom-slider {
  position: absolute;
  bottom: 0;
  width: 0;
  height: 6px;
  background: #ff5f14;
  transition: left 0.3s ease;
}
 
@media (min-width: 800px) {
  .nav-items h1,
  .bottom-slide h1 {
    font-size: 3rem;
  }
  .nav-items h3,
  .bottom-slide h3 {
    font-size: 1rem;
  }
 
  .navs {
    font-size: 1rem;
  }
}
@media (max-width: 765px) {
  .nav-items h1, .bottom-slide h1 {
    letter-spacing: 0ch;
  }
}
  </style>