Untitled

JavaScript error undefined object although object exist
<!DOCTYPE HTML>
<html>
    <head>
    </head>
    <body>
        <div class="full-details-box" name="full_details_box" id="full-details-box"></div>
        <hr />
        <script type='text/javascript'>
        function show_3136(){
            document.full_details_box.style.display='block';
        }
        show_3136();
        </script>
    </body>
</html>

document.full_details_box.style.display='block';

document.getElementById('full-details-box')...

function show_3136(){
     document.getElementById('full_details_box').style.display='block';
}

function show_3136() {
    document.getElementById("full-details-box").style.display = "block";
}

document.getElementById("full-details-box").style.display='block';

<html>
<head>
    <script type='text/javascript'>
    function showFormField(){
        document.forms[0].full_details_boxName.style.display='block';
        // or document.forms[0].elements["full_details_boxName"].style.display='block';
    }
    function showNamedField(){
        document.getElementsByName("full_details_boxName")[0].style.display='block';
    }
    function showFieldById(){
        document.getElementsById("full_details_boxID").style.display='block';
    }
    function showFieldByClassName(){ // does not work in all IE browsers
        document.getElementsByClassName("full_details_boxCLASS")[0].style.display='block';
    }
    </script>
</head>
<body>
<form>
  <input class="full-details-boxCLASS" name="full_details_boxName" id="full-details-boxID"/>
</form>
</body>
</html>