<img class="m-lazyload" data-src="imgUrl">

window.addEventListener('scroll', _delay, false);

function _delay() {
 clearTimeout(delay);
 delay = setTimeout(function () {
 _loadImage();
 }, time);
}

function _loadImage() {
 for (var i = imgList.length; i--;) {
 var el = imgList[i];
 if (_isShow(el)) {
  el.src = el.getAttribute('data-src');
  el.className = el.className.replace(new RegExp("(\\s|^)" + _selector.substring(1, _selector.length) + "(\\s|$)"), " ");
  imgList.splice(i, 1);
 }
 }
}

function _isShow(el) {
 var coords = el.getBoundingClientRect();
 return ( (coords.top >= 0 && coords.left >= 0 && coords.top) <= (window.innerHeight || document.documentElement.clientHeight) + parseInt(offset));
}

(function () {
 var imgList = [], // 页面所有img元素集合
 delay, // setTimeout 对象
 offset, //偏移量，用于指定图片距离可视区域多少距离，进行加载
 time, // 延迟载入时间
 _selector; // 选择器 默认为 .m-lazyload

 function _isShow(el) {
 var coords = el.getBoundingClientRect();
 return ( (coords.top >= 0 && coords.left >= 0 && coords.top) <= (window.innerHeight || document.documentElement.clientHeight) + parseInt(offset));
 }

 function _loadImage() {
 for (var i = imgList.length; i--;) {
  var el = imgList[i];
  if (_isShow(el)) {
  el.src = el.getAttribute('data-src');
  el.className = el.className.replace(new RegExp("(\\s|^)" + _selector.substring(1, _selector.length) + "(\\s|$)"), " ");
  imgList.splice(i, 1);
  }
 }
 }

 function _delay() {
 clearTimeout(delay);
 delay = setTimeout(function () {
  _loadImage();
 }, time);
 }

 function ImageLazyload(selector, options) {
 var defaults = options || {};
 offset = defaults.offset || 0;
 time = defaults.time || 250;
 _selector = selector || '.m-lazyload';
 this.getNode();
 _delay();//避免首次加载未触发touch事件,主动触发一次加载函数
 if (defaults.iScroll) {
  defaults.iScroll.on('scroll', _delay);
  defaults.iScroll.on('scrollEnd', _delay);
 } else {
  window.addEventListener('scroll', _delay, false);
 }
 }
 ImageLazyload.prototype.getNode = function () {
 imgList = [];
 var nodes = document.querySelectorAll(_selector);
 for (var i = 0, l = nodes.length; i < l; i++) {
  imgList.push(nodes[i]);
 }
 };
})();