问如何使元素在视口中可见？jQuery

EN

// get top positions and references to all images
var pos = $("img").map(function(){
  var $this = $(this);
  return {
    el: $this,
    top: $this.offset().top
  };
}).get();

// provide document scrolling
$(document).on("scroll", function() {

  $("img").removeClass("first-in-view");

  var scroll = $(this).scrollTop();
  var i = 0;
  while(pos[i].top < scroll) i++;

  pos[i].el.addClass("first-in-view");

}).scroll();