javascript 34 lines · 8 steps

Drag-to-reorder lists with the HTML5 drag API

A single delegated handler set turns any list into a drag-to-reorder widget that reports its new order.

Explained by highlit
Intermediate drag-and-drop event-delegation dom-manipulation closures
1function makeReorderableList(listEl, onReorder) {
2 let draggedItem = null;
3 
4 listEl.addEventListener('dragstart', (e) => {
5 const item = e.target.closest('[draggable="true"]');
6 if (!item) return;
7 draggedItem = item;
8 e.dataTransfer.effectAllowed = 'move';
9 e.dataTransfer.setData('text/plain', item.dataset.id);
10 requestAnimationFrame(() => item.classList.add('dragging'));
11 });
12 
13 listEl.addEventListener('dragover', (e) => {
14 e.preventDefault();
15 e.dataTransfer.dropEffect = 'move';
16 const target = e.target.closest('[draggable="true"]');
17 if (!target || target === draggedItem) return;
18 
19 const rect = target.getBoundingClientRect();
20 const after = e.clientY > rect.top + rect.height / 2;
21 listEl.insertBefore(draggedItem, after ? target.nextSibling : target);
22 });
23 
24 listEl.addEventListener('dragend', () => {
25 if (!draggedItem) return;
26 draggedItem.classList.remove('dragging');
27 draggedItem = null;
28 const order = [...listEl.querySelectorAll('[draggable="true"]')]
29 .map((el) => el.dataset.id);
30 onReorder(order);
31 });
32 
33 listEl.addEventListener('drop', (e) => e.preventDefault());
34}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Attaching listeners to the container instead of each item lets one closure track drag state across the whole list.
  2. 2Comparing the cursor's Y against an element's vertical midpoint decides whether to insert before or after it.
  3. 3Reading the live DOM order at dragend produces the canonical result without tracking moves manually.

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