How to change the content of an element with childNodes (Javascript)?

How can I change the content of an element with childNodes (Javascript)? I tried something but it did not work.

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Zitat</title>
        <script type="text/javascript">
            var htmlNode = document.documentElement;
            var emNode = htmlNode.childNodes[1].childNodes[0].childNodes[1].childNodes[1];
            emNode.innerHtml = "BBB";
        </script>
    </head>
    <body>
        <ul>
            <li>Hello World</li>
            <li>AAA <em>DDD</em> CCC.</li>
        </ul>
    </body>
</html>

Solution

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Zitat</title>
        <script>
            document.addEventListener("DOMContentLoaded", function (event) {
                var arrAllListTags = document.querySelectorAll("li");
                arrAllListTags[1].childNodes[1].textContent = "BBB";
            });
        </script>
    </head>
    <body>
        <ul>
            <li>Hello World</li>
            <li>AAA <em>DDD</em> CCC.</li>
        </ul>
    </body>
</html>