Dexie

Dexie.js — Local-First Patterns

Why Dexie

• Wraps IndexedDB with a clean Promise/async-await API
• useLiveQuery() auto-rerenders React components on data changes (no extra state management)
• Schema versioning with .upgrade() handles migrations for existing user data
• Typed tables via Table<T, PrimaryKey> — full TypeScript support
• IndexedDB storage cap: gigabytes (vs localStorage ~5 MB)

Setup

pnpm add dexie dexie-react-hooks

Database definition (lib/db.ts)

import Dexie, { type Table } from 'dexie';

export interface Item {
  id?: number;
  name: string;
  createdAt: number;
}

class AppDatabase extends Dexie {
  items!: Table<Item, number>;

  constructor() {
    super('AppDatabase');
    this.version(1).stores({
      items: '++id, name',
    });
  }
}

export const db = new AppDatabase();

• ++id — auto-increment primary key
• Only index fields you query/sort by; non-indexed fields are still stored

Schema migration

this.version(1).stores({ items: '++id, name' });

this.version(2).stores({ items: '++id, name, category' }).upgrade(tx =>
  tx.table('items').toCollection().modify(item => {
    item.category = item.category ?? 'uncategorized';
  })
);

• Always keep old versions — Dexie runs upgrades sequentially for users on older versions
• .modify() mutates in place; return value is ignored

Querying

const all = await db.items.toArray();
const filtered = await db.items.where('name').equals('foo').toArray();
const sorted = await db.items.orderBy('createdAt').toArray();
const one = await db.items.get(id);

Writes

const id = await db.items.add({ name: 'Foo', createdAt: Date.now() });
await db.items.update(id, { name: 'Bar' });
await db.items.put({ id: 1, name: 'Bar', createdAt: Date.now() }); // upsert
await db.items.delete(id);

React integration — useLiveQuery

import { useLiveQuery } from 'dexie-react-hooks';
import { db } from '@/lib/db';

export function ItemList() {
  const items = useLiveQuery(() => db.items.toArray(), []);

  if (!items) return <p>Loading…</p>;
  return <ul>{items.map(i => <li key={i.id}>{i.name}</li>)}</ul>;
}

• Returns undefined on first render — use as loading state
• Second arg is dependency array — include any variables used inside the query
• Re-renders automatically whenever the queried table changes

Transactions

await db.transaction('rw', db.items, async () => {
  await db.items.add({ ... });
  await db.items.update(someId, { ... });
});

Next.js / SSR constraint

• Dexie only runs client-side — use 'use client' directive or guard with typeof window !== 'undefined'
• Never call db.* in server components or static data-fetching functions

Gotchas

• Index only what you filter/sort on — over-indexing wastes space and slows writes
• useLiveQuery returns undefined initially — always handle the loading state
• Compound index: '[field1+field2]' in .stores() for multi-field queries
• Bulk ops: db.items.bulkAdd([...]) / db.items.bulkDelete([...]) for batch writes
• Version must only increase — never reuse or decrement a version number

References

• Docs: https://dexie.org/docs/
• React hooks: https://dexie.org/docs/dexie-react-hooks/useLiveQuery()