html link value retrieve by Js ajax send to php

html link value retrieve by Js ajax send to php

I have a html link with a value inside like this.
<a data-toggle='modal' data-id='1' href='#myModal' class='marker'
title='Edit'>Link</a>
I have a Js script that trigger a php that I want to send the value data-id
<script>
$(document).on("click", ".marker", function () {
var myBookId = $(this).data('id');
$.ajax({
type: "post",
url: "update.php", //
data: myBookId,
success: function(msg){
$("#thanks").html(msg)
},
error: function(){
alert("failure");
}
});
});
</script>
And in my php I have this
if (isset($_POST['myBookId'])) {
$emp_id = strip_tags($_POST['myBookId']);
echo $emp_id;
But something is wrong the value is not pass