jQuery(document).on('click', '.btn-details', (e) => {

jQuery(document).on('click', '.btn-details', function() {

jQuery(document).on('click', '.btn-details', (e) => {
   var btnDetails = e.target;
   var attr = btnDetails.data("attr");
}

jQuery(document).on('click', '.btn-details', function(e) {
   var btnDetails = e.target;
   var attr = btnDetails.data("attr");
}

$('div').click(function() {
  console.log(this) // the click target as expected
})

$('div').click(() => {
  console.log(this) // not the click target because jQuery can't bind it
})

$('div').click((e) => {
  console.log(e.currentTarget) // click target as expected
  console.log(this) // enclosing context - could be useful
}

(param1, param2, …, paramN) => { statements }

$(this).attr('data-test')