@thaitype/reorder

Pure reorder function for consistent and testable item ordering based on the order field.

✨ Features

• ⚙️ Pure function – works without DB or side effects.
• 🧪 100% unit-testable – ideal for CI pipelines and logic isolation.
• 📐 Order-aware – operates strictly on the order field, not array position.
• 🔄 Auto-renumbering – handles tight gaps and invalid values intelligently.
• ✅ Robust edge case handling – including missing/duplicate/invalid orders.

📦 Installation

npm install @thaitype/reorder
# or
pnpm add @thaitype/reorder

🧠 Use Case

Designed for reordering structures like chapters, lessons, or sublessons where the data model includes an { id, order? } field.

🔧 API

function reorderItems(
  items: OrderableItem[],
  moveId: string,
  targetIndex: number
): {
  changes: { id: string; order: number }[];
  orderedItems: OrderableItem[];
}

Types

export interface OrderableItem {
  id: string;
  order?: number;
}

📊 Algorithm Overview

1. Sort items by order ascending.

2. Remove the moveId item.

3. Insert it at targetIndex in the sorted array.

4. Recompute its order:

   • Between neighbors → use midpoint
   • Before first → next - 1
   • After last → previous + 1
   • Only item → assign 1

5. If new order too close → renumber all with step gaps (e.g. 10, 20, 30…).

6. Return:

   • changes[] for DB update
   • orderedItems[] for UI reference

🧪 Example

const items = [
  { id: 'A', order: 700 },
  { id: 'B', order: 200 },
  { id: 'C', order: 300 },
  { id: 'D', order: 100 },
  { id: 'E', order: 400 }
];

const result = reorderItems(items, 'A', 1);

Output:

{
  changes: [{ id: 'A', order: 150 }],
  orderedItems: [
    { id: 'D', order: 100 },
    { id: 'A', order: 150 },
    { id: 'B', order: 200 },
    { id: 'C', order: 300 },
    { id: 'E', order: 400 }
  ]
}

🧼 Edge Case Support

• ✅ Unsorted input
• ✅ Missing or undefined orders
• ✅ Duplicate or zero orders
• ✅ Insert at start, middle, end
• ✅ Auto-renumber when necessary

🧪 Tests

Run test suite with coverage:

pnpm test
pnpm test:coverage

📁 Exports

• reorderItems() — main reorder function
• sortItemsByOrder() — utility function to sort items

🧑‍💻 Development

pnpm install
pnpm build
pnpm test

To release:

pnpm release

📄 License

MIT © Thada Wangthammang