professional_javascript_for_web/ch11/ContainsExample02.htm

<!DOCTYPE html>
<html>
<head>
    <title>Contains Example 2</title>
    <script type="text/javascript" src="client.js"></script>
</head>
<body>

    <input type="button" value="Does html contain body?" onclick="getContains()">

    <script type="text/javascript">
    
        function contains(refNode, otherNode){
            if (typeof refNode.contains == "function" && 
                    (!client.engine.webkit || client.engine.webkit >= 522)){
                return refNode.contains(otherNode);
            } else if (typeof refNode.compareDocumentPosition == "function"){
                return !!(refNode.compareDocumentPosition(otherNode) & 16);
            } else {
                var node = otherNode.parentNode;
                do {
                    if (node === refNode){
                        return true;
                    } else {
                        node = node.parentNode;
                    }
                } while (node !== null);
                return false;
            }
        }
    
        function getContains(){
            alert(contains(document.documentElement, document.body));
            
        }

    </script>
</body>
</html>