codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>

    <script language="javascript" type="text/javascript">
// <!CDATA[

function Button1_onclick() 
{
    offtotalsub();
}

function offtotalsub() 
{//debugger;

    var stringa = new String;
    stringa = get('dirlist').value;
    stringa = stringa.slice(0, -1);
    var valori = new Array();

    valori = stringa.split("+");
    for (i = 0; i < valori.length; i++)
    {
        if(get(valori[i]))
        {
            get(valori[i]).innerHTML = "";
        }
    }
}

function get(s)
{
    return document.getElementById(s);
}

// ]]>
    </script>
</head>
<body>
    <input id="dirlist" type="text" value="ciao_22+ciao_33+ciao_42+" />
    <input id="Button1" type="button" value="button" onclick="return Button1_onclick()" />
    <div id="ciao_22">xxx</div>
    <div id="ciao_33">yyy</div>
    <div id="ciao_42">zzz</div>
</body>
</html>
funziona con IE7, Opera, Firefox, Chrome. Perciò rimando a quanto detto da Pastore12.