The conventional way of handling this doesn't play well with ES6. You can do this instead:
$('.delete').on('click', event => {
const clickedElement = $(event.target);
this.delete(clickedElement.data('id'));
});
Note that the event target will be the clicked element, which may not be the element you want (it could be a child that received the event). To get the actual element:
$('.delete').on('click', event => {
const clickedElement = $(event.target);
const targetElement = clickedElement.closest('.delete');
this.delete(targetElement.data('id'));
});