if (!$("tr").hasClass('hidebutton')) {
    var OriginalContent = $("#tabletask tr[data-id='" + parrentid + "'] > td:first-child").text();
    $("#tabletask tr[data-id='" + parrentid + "'] > td:first-child").html("<button class=hidebutton>-</button> " + OriginalContent + " ");
}

if(!$("tr button").hasClass("hidebutton")){
 $("#tabletask tr[data-id='" + parrentid + "'] > td:first-child").html('<button class="hidebutton">-</button> ' + OriginalContent);
}

html("<button class=hidebutton>-</button> " + OriginalContent + " ");

.html("<button class='hidebutton'>-</button> " + OriginalContent + " ");

$("tr").each(function( index, value ) {
    if (!$(this).hasClass('hidebutton')){
        console.log($(this,"td:first-child").text());
    }
});