ie8不支持lastIndexOf的解决方法

if (!Array.prototype.lastIndexOf) {
 Array.prototype.lastIndexOf = function(searchElement /*, fromIndex*/) {
 'use strict';

 if (this === void 0 || this === null) {
 throw new TypeError();
 }

 var n, k,
 t = Object(this),
 len = t.length >>> 0;
 if (len === 0) {
 return -1;
 }

 n = len - 1;
 if (arguments.length > 1) {
 n = Number(arguments[1]);
 if (n != n) {
 n = 0;
 }
 else if (n != 0 && n != (1 / 0) && n != -(1 / 0)) {
 n = (n > 0 || -1) * Math.floor(Math.abs(n));
 }
 }

 for (k = n >= 0
 ? Math.min(n, len - 1)
 : len - Math.abs(n); k >= 0; k--) {
 if (k in t && t[k] === searchElement) {
 return k;
 }
 }
 return -1;
 };
}