修改版zhanyouwei/m-lazy支持图片做背景的元素

 添加对元素tagName判断，若不是img元素怎把图片链接设置成background-image: url("图片地址")

/**
 * @author: Jason.占友伟 zhanyouwei@icloud.com
 * Created on 16/3/21.
 */

(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    define(function () {
      return factory(root);
    });
  } else if (typeof exports === 'object') {
    module.exports = factory;
  } else {
    root.mlazy = factory(root);
  }
})(window, function (root) {

  'use strict';

  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
    lazyTime,  // 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) <= (root.innerHeight || document.documentElement.clientHeight) + parseInt(offset));
  }

  function _loadImage() {
    for (var i = imgList.length; i--;) {
      var el = imgList[i];
      if (_isShow(el)) {
        var src = el.getAttribute('data-src');
        if ('img' === el.tagName.toLowerCase()) {
          el.src = src;
        } else {
          el.style.backgroundImage = 'url(' + 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();
    }, lazyTime);
  }

  function mlazy(selector, options) {
    var defaults = options || {};
    offset = defaults.offset || 100;
    lazyTime = defaults.lazyTime || 100;
    _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('scrollEnd', _delay);
    } else {
      root.addEventListener('scroll', _delay, false);
    }
  }

  mlazy.prototype.getNode = function () {
    imgList = [];
    var nodes = document.querySelectorAll(_selector);
    for (var i = 0, l = nodes.length; i < l; i++) {
      imgList.push(nodes[i]);
    }
  };

  return mlazy;
});