Persistence

In tldraw, persistence means storing information about the editor's state to a database and then restoring it later.

The simplest implementation is the browser's local storage. But this also provides the hooks for a sync engine, which can send realtime incremenal updates the canvas to your backend server, allowing multiple people to collaborate on the canvas.

The `"persistenceKey"` prop

Both the <Tldraw> or <TldrawEditor> components support local persistence and cross-tab synchronization via the persistenceKey prop. Passing a value to this prop will persist the contents of the editor locally to the browser's IndexedDb.

import { Tldraw } from 'tldraw'
import 'tldraw/tldraw.css'

export default function () {
	return (
		<div style={{ position: 'fixed', inset: 0 }}>
			<Tldraw persistenceKey="my-persistence-key" />
		</div>
	)
}

Using a persistenceKey will synchronize data automatically with any other tldraw component with the same persistenceKey prop, even if that component is in a different browser tab.

import { Tldraw } from 'tldraw'
import 'tldraw/tldraw.css'

export default function () {
	return (
		<div style={{ position: 'fixed', inset: 0 }}>
			<div style={{ width: '50%', height: '100%' }}>
				<Tldraw persistenceKey="my-persistence-key" />
			</div>
			<div style={{ width: '50%', height: '100%' }}>
				<Tldraw persistenceKey="my-persistence-key" />
			</div>
		</div>
	)
}

In the example above, both editors would synchronize their document locally. They would still have two independent instance states (e.g. selections) but the document would be kept in sync and persisted under the same key.

State Snapshots

You can get a JSON snapshot of the document content and the user 'session' state using the getSnapshot function.

function SaveButton({ documentId, userId }) {
	const editor = useEditor()
	return (
		<button
			onClick={() => {
				const { document, session } = getSnapshot(editor.store)
				// If you are building a multi-user app, you probably want to store
				// the document and session states separately because the
				// session state is user-specific and normally shouldn't be shared.
				await saveDocumentState(documentId, document)
				await saveSessionState(documentId, userId, session)
			}}
		>
			Save
		</button>
	)
}

To load the snapshot back into an existing editor, use the loadSnapshot function.

function LoadButton({ documentId, userId }) {
	const editor = useEditor()
	return (
		<button
			onClick={() => {
				const document = await loadDocumentState(documentId)
				const session = await loadSessionState(documentId, userId)
				editor.setCurrentTool('select') // need to reset tool state separately
				loadSnapshot(editor.store, { document, session })
			}}
		>
			Load
		</button>
	)
}

You can also pass a snapshot as a prop to set the initial editor state.

function MyApp({ userId, documentId }) {
	const [snapshot, setSnapshot] = useState(null)

	useEffect(() => {
		async function load() {
			const document = await getDocumentState(documentId)
			const session = await getSessionState(documentId, userId)
			setSnapshot({ document, session })
		}

		load()
	}, [documentId, userId])

	return snapshot ? <Tldraw snapshot={snapshot} /> : null
}

When tldraw loads a snapshot, it will run any necessary migrations to bring the data up to the latest tldraw schema version.

The `"store"` prop

While it's possible to load the editor and then load data into its store, we've found it best to create the store, set its data, and then pass the store into the editor.

The store property of the <Tldraw> / <TldrawEditor> components accepts a store that you've defined outside of the component.

export default function () {
	const [store] = useState(() => {
		// Create the store
		const newStore = createTLStore()

		// Get the snapshot
		const stringified = localStorage.getItem('my-editor-snapshot')
		const snapshot = JSON.parse(stringified)

		// Load the snapshot
		loadSnapshot(newStore, snapshot)

		return newStore
	})

	return <Tldraw persistenceKey="my-persistence-key" store={store} />
}

Sometimes you won't be able to access the store's data synchronously. To handle this case, the store property also accepts a TLStoreWithStatus.

export default function () {
	const [storeWithStatus, setStoreWithStatus] = useState<TLStoreWithStatus>({
		status: 'loading',
	})

	useEffect(() => {
		let cancelled = false
		async function loadRemoteSnapshot() {
			// Get the snapshot
			const snapshot = await getRemoteSnapshot()
			if (cancelled) return

			// Create the store
			const newStore = createTLStore()

			// Load the snapshot
			loadSnapshot(newStore, snapshot)

			// Update the store with status
			setStoreWithStatus({
				store: newStore,
				status: 'ready',
			})
		}

		loadRemoteSnapshot()

		return () => {
			cancelled = true
		}
	})

	return <Tldraw persistenceKey="my-persistence-key" store={storeWithStatus} />
}

For a good example of this pattern, see the yjs-example.

Listening for changes

You can listen for incremental updates to the document state by calling editor.store.listen, e.g.

const unlisten = editor.store.listen(
	(update) => {
		console.log('update', update)
	},
	{ scope: 'document', source: 'user' }
)

These updates contain information about which records were added, removed, and updated. See HistoryEntry

The scope filter can be used to listen for changes to a specific record scope, e.g. document, session, presence, or all.

The source filter can be used to listen for changes from a specific source, e.g. user, remote, or all. (See Store.mergeRemoteChanges for more information on remote changes.)

Note that these incremental updates do not include the schema version. You should make sure that you keep a record of the latest schema version for your snapshots.

You can get the schema version by calling editor.store.schema.serialize() and the returned value can replace the schema property in the snapshot next time you need to load a snapshot. The schema does not change at runtime so you only need to do this once per session.

Handling remote changes

If you need to synchronize changes from a remote source, e.g. a multiplayer backend, you can use the editor.store.mergeRemoteChanges method. This will 'tag' the changes with the source property as 'remote' so you can filter them out when listening for changes.

myRemoteSource.on('change', (changes) => {
	editor.store.mergeRemoteChanges(() => {
		changes.forEach((change) => {
			// Apply the changes to the store
			editor.store.put(/* ... */)
		})
	})
})

Migrations

Tldraw uses migrations to bring data from old snapshots up to date. These run automatically when calling loadSnapshot.

Running migrations manually

If you need to run migrations on a snapshot without loading it into the store, you can call StoreSchema.migrateStoreSnapshot directly.

import { createTLSchema } from 'tldraw'

const snapshot = await getSnapshotFromSomewhere()
const migrationResult = createTLSchema().migrateStoreSnapshot(snapshot)
if (migrationResult.type === 'success') {
	console.log('Migrated snapshot', migrationResult.value)
} else {
	console.error('Migration failed', migrationResult.reason)
}

Custom migrations

Tldraw supports a couple of ways of adding custom data types to the tldraw store:

Custom shape types
meta properties on all of our built-in record types.

You might wish to migrate your custom data types over time as you make changes to them.

To enable this, tldraw provides two ways to add custom migrations:

Shape props migrations, specifically for migrating the shape.props objects on your custom shape types.
The migrations config option, which is more general purpose but much less commonly needed. This will allow you to migrate any data in the store.

Shape props migrations

If you have a custom shape type, you can define a migrations property on the shape util class. Use the createShapePropsMigrationSequence helper to define this property.

import { createShapePropsMigrationSequence, createShapePropsMigrationIds, ShapeUtil } from 'tldraw'

// Migrations must start a 1 and be sequential integers.
const Versions = createShapePropMigrationIds('custom-shape', {
	AddColor: 1,
})

class MyCustomShapeUtil extends ShapeUtil {
	static type = 'custom-shape'
	static migrations = createShapePropsMigrationSequence({
		sequence: [
			{
				id: Versions.AddColor,
				up(props) {
					// set the default color
					props.color = 'black'
				},
			},
		],
	})

	// ...
}

The `migrations` config option

First create a set of migration ids.

import { createMigrationIds } from 'tldraw'

// The first argument is a unique namespace for your migration sequence.
// We recommend using a reverse domain name, e.g. we use 'com.tldraw.foo.bar'
const SEQUENCE_ID = 'com.example.my-app'

const Versions = createMigrationIds(SEQUENCE_ID, {
	// Migrations must start at 1 and be sequential integers.
	AddColor: 1,
})

Then create a migration sequence.

import { createMigrationSequence, isShape } from 'tldraw'

const myMigrations = createMigrationSequence({
	sequenceId: SEQUENCE_ID,
	sequence: [
		{
			id: Versions.AddColor,
			// Scope can be one of
			// - 'store' to have the up function called on the whole snapshot at once
			// - 'record' to have the up function called on each record individually
			scope: 'record',
			// if scope is 'record', you can filter which records the migration runs on
			filter: (record) => isShape(record) && record.type === 'custom-shape',
			up(record) {
				record.props.color = 'black'
			},
		},
	],
})

And finally pass your migrations in to tldraw via the migrations config option. There are a few places where you might need to do this, depending on how specialized your usage of Tldraw is:

// When rendering the Tldraw component
<Tldraw
  ...
	migrations={[myMigrations]}
	/>

// or when creating the store
store = createTLStore({
	...
	migrations: [myMigrations],
})

// or when creating the schema
schema = createTLSchema({
	...
	migrations: [myMigrations],
})

Updating legacy shape migrations (defineMigrations)

You can convert your legacy migrations to the new migrations format by the following process:

Wrap your version numbers in createShapePropsMigrationIds

- const Versions = {
+ const Versions = createShapePropMigrationIds('custom-shape', {
    AddColor: 1
- }
+ })

Replace your defineMigrations call with createShapePropsMigrationSequence

const migrations = defineMigrations({
	currentVersion: Versions.AddColor,
	migrators: {
		[Versions.AddColor]: {
			up: (shape: any) => ({ ...shape, props: { ...shape.props, color: 'black' } }),
			down: ({ props: { color, ...props }, ...shape }: any) => ({ ...shape, props }),
		},
	},
})

Becomes

const migrations = createShapePropsMigrationSequence({
	sequence: [
		{
			id: Versions.AddColor,
			// [!!!] You no longer have access to the top-level shape object.
			// Only the shape.props object is passed in to the migrator function.
			up(props) {
				// [!!!] You no longer need to return a new copy of the shape object.
				// Instead, you can modify the props object in place.
				props.color = 'black'
			},
			// [!!!] You no longer need to specify a down migration.
		},
	],
})

Examples

Local persistence

Tldraw ships with a local-only sync engine based on IndexedDb and BroadcastChannel called TLLocalSyncClient.

Shape props migrations example

Our custom-config example shows how to add custom shape props migrations to the tldraw store.

Meta properties migrations example

Our custom-config example shows how to add custom migrations to the tldraw store.

The "persistenceKey" prop