export default {
  inserted: function(el, binding) {
    el.onclick = function() {
      let total;
      if (binding.value == 0) {
        total = 0;
      } else {

        total = document.getElementById(`anchor-${binding.value}`).offsetTop;
      }
      let distance = document.documentElement.scrollTop || document.body.scrollTop;
      let step = total / 50;
      if (total > distance) {
        (function smoothDown() {
          if (distance < total) {
            distance += step;
            document.documentElement.scrollTop = distance;
            setTimeout(smoothDown, 5);
          } else {
            document.documentElement.scrollTop = total;
          }
        })();
      } else {
        let newTotal = distance - total;
        step = newTotal / 50;
        (function smoothUp() {
          if (distance > total) {
            distance -= step;
            document.documentElement.scrollTop = distance;
            setTimeout(smoothUp, 5);
          } else {
            document.documentElement.scrollTop = total;
          }
        })();
      }

    }
  }
}

//定义锚点跳转 
Vue.directive(‘anchor', anchorFunc); 

v-anchor = “传入的value”