解决了IE8不支持数组的indexOf方法

 1 if (!Array.prototype.indexOf) {
 2     Array.prototype.indexOf = function(elt /*, from*/ ) {
 3         var len = this.length >>> 0;
 4         var from = Number(arguments[1]) || 0;
 5         from = (from < 0) ? Math.ceil(from) : Math.floor(from);
 6         if (from < 0)
 7             from += len;
 8         for (; from < len; from++) {
 9             if (from in this &&
10                 this[from] === elt)
11                 return from;
12         }
13         return -1;
14     };
15 }