ie8的兼容

1、IE8以下不支持getElementsByClassName方法
//解决IE8之类不支持getElementsByClassName
if (!document.getElementsByClassName) {
    document.getElementsByClassName = function (className, element) {
        var children = (element || document).getElementsByTagName('*');
        var elements = new Array();
        for (var i = 0; i < children.length; i++) {
            var child = children[i];
            var classNames = child.className.split(' ');
            for (var j = 0; j < classNames.length; j++) {
                if (classNames[j] == className) {
                    elements.push(child);
                    break;
                }
            }
        }
        return elements;
    };
}

2、IE8不支持数组的indexOf方法 如何解决
//添加数组IndexOf方法
if (!Array.prototype.indexOf){
  Array.prototype.indexOf = function(elt /*, from*/){
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0)
         ? Math.ceil(from)
         : Math.floor(from);
    if (from < 0)
      from += len;

    for (; from < len; from++){
      if (from in this && this[from] === elt)
        return from;
    }
    return -1;
  };
}

3、nth-child
ul li:nth-child(1){
      color:#fff;
  }/*选取第一个li*/
  ul li:nth-child(odd){
      color:#fff;
  }/*选取偶数*/
  ul li:nth-child(even){
      color:#fff;
  }/*选取奇数*/
  ul li:nth-child(3n+1){
      color:#fff;
  }/*选取3n+1个元素*/
  ie8不兼容nth-child()
ul li:first-child{
    color:#fff;
}/*选取第一个li*/
ul li:first-child+li+li{
    color:#fff;
}/*选取第三个li*/

4、ie8不兼容opacity
filter: progid:DXImageTransform.Microsoft.Alpha(opacity=70);