String.truncate.js

String.implement({
    truncate: function(max, trail, separator){
        var s = this.trim();
        if (s.length <= max) return s;
       
        separator = $pick(separator, ' ');
        if (separator)
            s = s.substr(0, max + 1).substr(0, s.lastIndexOf(separator));
        else
            s = s.substr(0, max);
       
        return s + $pick(trail, '...');
    }
});