Saber el viewport de Bootstrap 3: xs, sm, md y lg. FROM: http://stackoverflow.com/questions/14441456/how-to-detect-which-device-view-youre-on-using-twitter-bootstrap-api#answer-15150381
function findBootstrapEnvironment() {
    var envs = ['xs', 'sm', 'md', 'lg'],
        $el = $('<div>'),
        i = 0,
        env;
    $el.appendTo($('body'));
    for (i = envs.length - 1; i >= 0; i--) {
        env = envs[i];
        $el.addClass('hidden-' + env);
        if ($el.is(':hidden')) {
            $el.remove();
            return env;
        }
    }
}