append() is preceded by the object to be selected, followed by the element content to be inserted into the object.
The front of appendTo() is the element content to be inserted and is a Jquery object, and the following is the object to be selected.
Example:
$('#a').append('content');
$('<div>content</div>').appendTo($('#a'));
Note that appendTo must be preceded by a Jquery object.
The appendChild(Node) method generally adds a node after the last child node of the specified element node.
But if Node is a DOM object in the page, then it is either adding the node or directly moving the node.
appendChild can be understood as moving an element. If you want to make a copy of the past, you must clone it in advance.