问Jquery脚本在IE 7-8中不起作用

EN

<script type="text/javascript" src="{{ STATIC_URL }}js/jquery-1.7.2.min.js"></script>
<script type="text/javascript" src="{{ STATIC_URL }}js/jquery.red-first.js"></script>

(function($) {
    $.fn.redFirst = function() {
        var city = $(this).text().trim();
        var newCity;
        if (city == 'г. Москва') { city = 'Москва'; }
        if (city == 'г. Санкт-Петербург') { city = 'Санкт-Петербург'; }
        var cityWords = city.split(' ');
        if (cityWords.length == 1) {
            newCity = '<span class="red">' + city[0] + '</span>';
            newCity = newCity + city.slice(1);;
        } else {
            newCity = '<span class="red">' + cityWords[0] + '</span>';
            delete cityWords[0];
            newCity = newCity + cityWords.join(' ');
        }
        $(this).html(newCity);
        return this;
    };
})(jQuery);

$(document).ready(function(){
    $('#city').redFirst();
    $('#choose_reg_city').redFirst();
    $('#authorization #region').redFirst();
});