StoreBeforeChangeHandler • tldraw Docs

Handler function called before a record is updated in the store. The handler receives the current and new versions of the record and can return a modified version or the original to prevent the change.

type StoreBeforeChangeHandler<R extends UnknownRecord> = (
  prev: R,
  next: R,
  source: 'remote' | 'user'
) => R

Example

const handler: StoreBeforeChangeHandler<ShapeRecord> = (prev, next, source) => {
  // Prevent shapes from being moved outside the canvas bounds
  if (next.x < 0 || next.y < 0) {
    return prev // Block the change
  }
  return next
}

Parameters

Name	Description
`prev`	The current version of the record in the store
`next`	The proposed new version of the record
`source`	Whether the change originated from 'user' interaction or 'remote' synchronization