how to create show more item in javascript

//start the javascript
$(function () {
    $('span').click(function () {
        $('#datalist li:hidden').slice(0, 2).show();
        if ($('#datalist li').length == $('#datalist li:visible').length) {
            $('span ').hide();
        }
    });
});
//end the javascript


//start the css
ul li:nth-child(n+3) {
    display:none;
}
ul li {
    border: 1px solid #aaa;
}
span {
    cursor: pointer;
    color: #f00;
}
//end the css



//start the html
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<ul id="datalist">
  <li>dataset1</li>
  <li>dataset1</li>
  <li>dataset2</li>
  <li>dataset2</li>
  <li>dataset3</li>
  <li>dataset3</li>
  <li>dataset4</li>
  <li>dataset4</li>
  <li>dataset5</li>
  <li>dataset5</li>
</ul>
<span>readmore</span>


//end the html