使用 javascript substring() 创建阅读更多链接

I'm developing a Classic ASP page that pulls some content from a database and creates a Read more link after the first 100 characters as follows;

<div class="contentdetail"><%=StripHTML(rspropertyresults.Fields.Item("ContentDetails").Value)%></div>

<script type="text/javascript">
    $(function() {

        var cutoff = 200;
        var text = $('div.contentdetail').text();
        var rest = $('div.contentdetail').text().substring(cutoff);
        if (text.length > 200) {
          var period = rest.indexOf('.');
          var space = rest.indexOf(' ');
          cutoff += Math.max(Math.min(period, space), 0);
        }

        var visibleText = $('div.contentdetail').text().substring(0, cutoff);

        $('div.contentdetail')
            .html(visibleText + ('<span>' + rest + '</span>'))
            .append('<a title="Read More" style="font-weight:bold;display: block; cursor: pointer;">Read More&hellip;</a>')
            .click(function() {
                $(this).find('span').toggle();
                $(this).find('a:last').hide();
            });

        $('div.contentdetail span').hide();
    });
</script>

但是，脚本显然只是在 100 个字符后截断了文本.最好我希望它继续写文本，直到第一个句号或空格，例如.这可以吗?

var cutoff = 100;
var text = $('div.contentdetail').text();
var rest = text.substring(cutoff);
if (text.length > cutoff) {
  var period = rest.indexOf('.');
  var space = rest.indexOf(' ');
  cutoff += Math.max(Math.min(period, space), 0);
}
// Assign the rest again, because we recalculated the cutoff
rest = text.substring(cutoff);
var visibleText = $('div.contentdetail').text().substring(0, cutoff);