Detailed explanation of image lazy loading imgLazyLoading.js

//懒加载对象目标代码
<img originalSrc="__PUBLIC__/images/home/icon_pingtuan.png">
//引用本地js
<script src="__PUBLIC__/js/imgLazyLoading.min.js"></script>
<script src="__PUBLIC__/js/imgLazyLoading.js"></script>

jQuery.fn.extend({
  delayLoading: function (a) {
    function g(d) {
      var b, c;
      if (a.container === undefined || a.container === window) {
        b = $(window).scrollTop();
        c = $(window).height() + $(window).scrollTop()
      } else {
        b = $(a.container).offset().top;
        c = $(a.container).offset().top + $(a.container).height()
      }
      return d.offset().top + d.height() + a.beforehand >= b && c >= d.offset().top - a.beforehand
    }

    function h(d) {
      var b, c;
      if (a.container === undefined || a.container === window) {
        b = $(window).scrollLeft();
        c = $(window).width() + $(window).scrollLeft()
      } else {
        b = $(a.container).offset().left;
        c = $(a.container).offset().left + $(a.container).width()
      }
      return d.offset().left + d.width() + a.beforehand >= b && c >= d.offset().left - a.beforehand
    }

    function f() {
      e.filter("img[" + a.imgSrcAttr + "]").each(function (d, b) {
        if ($(b).attr(a.imgSrcAttr) !== undefined && $(b).attr(a.imgSrcAttr) !== null && $(b).attr(a.imgSrcAttr) !== "" && g($(b)) && h($(b))) {
          var c = new Image;
          c.onload = function () {
            $(b).attr("src", c.src);
            a.duration !== 0 && $(b).hide().fadeIn(a.duration);
            $(b).removeAttr(a.imgSrcAttr);
            a.success($(b))
          };
          c.onerror = function () {
            $(b).attr("src",
              a.errorImg);
            $(b).removeAttr(a.imgSrcAttr);
            a.error($(b))
          };
          c.src = $(b).attr(a.imgSrcAttr)
        }
      })
    }

    a = jQuery.extend({
      defaultImg: "",
      errorImg: "",
      imgSrcAttr: "originalSrc",
      beforehand: 0,
      event: "scroll",
      duration: "normal",
      container: window,
      success: function () {
      },
      error: function () {
      }
    }, a || {});
    if (a.errorImg === undefined || a.errorImg === null || a.errorImg === "")a.errorImg = a.defaultImg;
    var e = $(this);
    if (e.attr("src") === undefined || e.attr("src") === null || e.attr("src") === "")e.attr("src", a.defaultImg);
    f();
    $(a.container).bind(a.event, function () {
      f()
    })
  }
});

$(function () {
  $("img").delayLoading({
    //defaultImg: "__PUBLIC__/images/img/loading.gif",      // 预加载前显示的图片
    errorImg: "",            // 读取图片错误时替换图片(默认：与defaultImg一样)
    imgSrcAttr: "originalSrc",      // 记录图片路径的属性(默认：originalSrc，页面img的src属性也要替换为originalSrc)
    beforehand: 0,            // 预先提前多少像素加载图片(默认：0)
    event: "scroll",           // 触发加载图片事件(默认：scroll)
    duration: "normal",         // 三种预定淡出(入)速度之一的字符串("slow", "normal", or "fast")或表示动画时长的毫秒数值(如：1000),默认:"normal"
    container: window,          // 对象加载的位置容器(默认：window)
    success: function (imgObj) { },   // 加载图片成功后的回调函数(默认：不执行任何操作)
    error: function (imgObj) { }     // 加载图片失败后的回调函数(默认：不执行任何操作)
  });
});