无法在导航栏中实现的jquery向下滑动功能

<script src="https://cdn.jsdelivr.net/npm/jquery/dist/jquery.min.js"></script>

<nav>
  <ul>
    <li><a href="#section1">Section 1</a></li>
    <li><a href="#section2">Section 2</a></li>
    <li><a href="#section3">Section 3</a></li>
  </ul>
</nav>

<section id="section1">
  <!-- Section 1 content -->
</section>

<section id="section2">
  <!-- Section 2 content -->
</section>

<section id="section3">
  <!-- Section 3 content -->
</section>

$(document).ready(function() {
  $('a[href^="#"]').on('click', function(event) {
    var target = $(this.getAttribute('href'));
    if (target.length) {
      event.preventDefault();
      $('html, body').stop().animate({
        scrollTop: target.offset().top
      }, 1000);
    }
  });
});