var str = "<sup><div class=\"he's\"/></sup><span id=\"cs\"/>";

function removeCloseTag(str) {

    var regCloseTag = /<[^>]+\/>/,

        regTagName = /[^<][^\s]+/,

        tmp,

        tagName;

    while((tmp = str.match(regCloseTag)) && tmp.length > 0){

        tagName = tmp[0].match(regTagName);

        str = str.replace(/\/>/, '></'+tagName+'>');

    }

    return str;

}

var res = removeCloseTag(str); //<sup><div class="he's"></div></sup><span id="cs"></span>