This function allows you to pass two variables that represent ID of two elements on your page. What you click on one of them it hide it and shows another one.

gistfile1.js

    <script type="text/javascript">
/* Source: http://www.apphp.com/index.php?snippet=javascript-toggle-elements */
    function toggle(id, id2){  
        var toggle_one = document.getElementById(id);  
        var toggle_two = document.getElementById(id2);  
        if(toggle_one.style.display == "block"){  
            toggle_one.style.display = "none";  
            toggle_two.innerHTML = "Show";  
        }else{  
            toggle_one.style.display = "block";  
            toggle_two.innerHTML = "Hide";  
        }  
    }
    </script>
     
    <a href="#" id="tlink" onclick="toggle('comments', 'tlink');">Show</a> Comments<br><br>  
    <div id="comments" style="display:none;padding 10px;">Now you can see the comments</div>