Why Browser Drag-and-Drop Silently Fails and How to Fix It

A common but non-obvious bug in HTML drag-and-drop causes dropped elements to snap back with no console error, leaving developers puzzled. The root cause is that browsers block drops on all elements by default, and the only way to unlock a valid drop target is to call e.preventDefault() inside a dragover event listener. Without this single line, the drop event never fires regardless of how correctly the rest of the code is written. A secondary issue involves flickering highlight states on drop zones that contain child elements, caused by dragenter and dragleave events firing at every DOM boundary crossing. This can be resolved by checking the leave event's relatedTarget to confirm the cursor has actually exited the drop zone entirely.