Error: Failed to execute 'appendChild' on 'Node': parameter 1 is not of type 'Node'

It's actually a simple answer.

Your function is returning a string rather than the div node. appendChild can only append a node.

For example, if you try to appendChild the string:

var z = '<p>test satu dua tiga</p>'; // is a string 
document.body.appendChild(z);

The above code will never work. What will work is:

var z = document.createElement('p'); // is a node
z.innerHTML = 'test satu dua tiga';
document.body.appendChild(z);

This can happen if you accidentally are not dragging the element that does have an id assigned (for example you are dragging the surrounding element). In that case the ID is empty and the function drag() is assigning an empty value which is then passed to drop() and fails there.

Try assigning the ids to all of your elements, including the tds, divs, or whatever is around your draggable element.