js代码

<script>
function customWayPoint(className, addClassName, customOffset) {
  var waypoints = $(className).waypoint({
    handler: function(direction) {
      if (direction == "down") {
        $(className).addClass(addClassName);
      } else {
        $(className).removeClass(addClassName);
      }
    },
    offset: customOffset
  });
}

var defaultOffset = '50%';

for (i = 0; i < 17; i++) {
  customWayPoint('.timeline__item--' + i, 'timeline__item-bg', defaultOffset);
}
</script>