导航栏是如何使用vanilla javascript实现平滑滚动的？

const links = document.querySelectorAll('.nav-link');
links.forEach(link => {
  link.addEventListener('click', smoothScroll);
});

function smoothScroll(event) {
  event.preventDefault();
  
  const targetId = this.getAttribute('href');
  const targetElement = document.querySelector(targetId);
  const targetPosition = targetElement.offsetTop;
  
  // ...
}

function smoothScroll(event) {
  event.preventDefault();
  
  const targetId = this.getAttribute('href');
  const targetElement = document.querySelector(targetId);
  const targetPosition = targetElement.offsetTop;
  
  const startPosition = window.pageYOffset;
  const distance = targetPosition - startPosition;
  const duration = 1000; // 滚动持续时间，单位为毫秒
  
  let startTimestamp = null;
  function animation(currentTimestamp) {
    if (startTimestamp === null) startTimestamp = currentTimestamp;
    const progress = currentTimestamp - startTimestamp;
    
    window.scrollTo(0, easeInOutCubic(progress, startPosition, distance, duration));
    
    if (progress < duration) {
      requestAnimationFrame(animation);
    }
  }
  
  requestAnimationFrame(animation);
}

function easeInOutCubic(t, b, c, d) {
  t /= d / 2;
  if (t < 1) return c / 2 * t * t * t + b;
  t -= 2;
  return c / 2 * (t * t * t + 2) + b;
}