IE浏览器不兼容indexOf问题

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;
    };
}

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;    };}