<script>
function StripTags(strMod){
    if(arguments.length<3) strMod=strMod.replace(/<\/?(?!\!)[^>]*>/gi, '');
    else{
        var IsAllowed=arguments[1];
        var Specified=eval("["+arguments[2]+"]");
        if(IsAllowed){
            var strRegExp='</?(?!(' + Specified.join('|') + '))\b[^>]*>';
            strMod=strMod.replace(new RegExp(strRegExp, 'gi'), '');
        }else{
            var strRegExp='</?(' + Specified.join('|') + ')\b[^>]*>';
            strMod=strMod.replace(new RegExp(strRegExp, 'gi'), '');
        }
    }
    return strMod;
}

var txt = ' <span class="text_main_4">36 </span>';
var matches = txt.match(/<span class=.*>.*<\/span>/g);
for (i in matches) {
  alert(i + ' : ' + StripTags(matches[i]));
}
</script>