<div id="successAndErrorMessages"></div>

<div id="successAndErrorMessages"><div class="portlet-msg-error">This is an error message</div></div>

document.getElementById("successAndErrorMessages").value="someContent";

document.getElementById("successAndErrorMessages").innerHTML="someContent";

<div id=successAndErrorMessages-1>100% OK</div>
    <div id=successAndErrorMessages-2>This is an error mssg!</div>

$("#successAndErrorMessages-1").css('display', 'none')
 $("#successAndErrorMessages-2").css('display', '')

var text = "example";
 $(this).contents()[0].data = text;