Edit in JSFiddle

// source code for $.fn.getComments()
$(function () {
/**
* $.fn.getComments() is used to extract the html comments from a HTML elements.
* 
* @author Larry Battle <http://bateru.com/news/contact-me>
* @license MIT
* @date June 11, 2012
* @version 0.1
* @args {boolean} asArray - If true, returns an array of the comments values. 
        Otherwise returns jquery objects of the node comments.
* @example <code><pre>
HTML:
<div id="example">I am a div. <!--Duh!--></div>

Javascript: 
$("#example").getComments(true) // returns [ "Duh!" ]
</pre></code>
*/
    var getCommentsFromEl = function (el, asArray) {
        var result,
        $el = $(el).contents();
        result = $el.filter(function () {
                return this.nodeType == 8;
            });
        if (asArray) {
            result = $.makeArray(result.map(function () {
                        return this.nodeValue;
                    }));
        }
        return result;
    };
    $.fn.getComments = function (asArray) {
        return getCommentsFromEl(this, asArray);
    };
});





// Hide testArea for testing purposes.
$("#testArea").hide();

// test cases
$(function () {

    test("test $.fn.getComments() with elements with no comments", function () {
        var func = function (str) {
            return $("#testArea").html(str).getComments();
        };
        var str;
        
        str = "";
        equal(func(str).length, 0);
        
        str = "<div>I'm a div</div>";
        equal(func(str).length, 0);
        
        str = "No html tags in here.";
        equal(func(str).length, 0);
    });
    
    test("test $.fn.getComments() with elements with comments", function () {
        var func = function (str) {
            return $("#testArea").html(str).getComments();
        };
        var str;
        str = "<!--1-->";
        equal(func(str).length, 1);
        
        str = "<!--1--><div>This is a div</div><!--2-->";
        equal(func(str).length, 2);
        
        str = "<a href='#'>This is a link</a>.<!--1--><span> ok </span>, then <!--2--> <b>be</b> <!--3--><b>bold</b>";
        equal(func(str).length, 3);
    });
    
    test("test $.fn.getComments() with elements with comments in array format", function () {
        var func = function (str) {
            return $("#testArea").html(str).getComments(true);
        };
        var str;
        str = "<!--3-->";
        deepEqual(func(str), ["3"]);
        
        str = "Test is ? <!--<div><b>hidden content</b></div>-->";
        deepEqual(func(str), ["<div><b>hidden content</b></div>"]);
        
        str = "<!--1--><div>This is a div</div><!--2--><span>This is a span</span><!--3--><b>ok></b><!--4-->...";
        deepEqual(func(str), ["1", "2", "3", "4"]);
    });
});

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
                    "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <link rel="stylesheet" href="http://code.jquery.com/qunit/git/qunit.css" type="text/css" media="screen" />
    </head>
    <body>
        <div id="testArea"></div>
        <h1 id="qunit-header">$.fn.getComments example</h1>
        <h2 id="qunit-banner"></h2>
        <div id="qunit-testrunner-toolbar"></div>
        <h2 id="qunit-userAgent"></h2>
        <ol id="qunit-tests"></ol>
        <div id="qunit-fixture">test markup, will be hidden</div>
        <script src="http://code.jquery.com/jquery-latest.js"></script>
        <script type="text/javascript" src="http://code.jquery.com/qunit/git/qunit.js"></script>  
    </body>
</html>