10.1.4 • Public • Published

Array Type for Yjs

This plugins provides a shareable Array type. You can insert and delete objects in y-array. The objects must either be a custom type, or fulfill the following property: v equals JSON.parse(JSON.stringify(v)) (according to your definition of equality)

Use it!

Install this with bower or npm.

bower install y-array --save
npm install y-array --save

Array Object

  • .insert(position, contents)
    • Insert an array of content at a position
    • You can also insert types array.insert(0, Y.Map)
    • If not a shared type, the content should fulfill the following property: content equals JSON.parse(JSON.stringify(content)) (according to your notion of equality)
  • .push(content)
    • Insert content at the end of the Array
    • Also see .insert(..)
  • .delete(position, length)
    • Delete content. The length parameter is optional and defaults to 1
  • .toArray()
    • Retrieve the complete content as an array
  • .get(position)
    • Retrieve content from a position
  • .observe(function observer(event){..})
    • The observer is called whenever something on this array changes
    • Throws insert, and delete events (event.type)
    • Insert event example: {type: 'insert', index: 0, values: [0, 1, 2], length: 3}
    • Delete event example: {type: 'delete', index: 0, oldValues: [0, 1, 2], length: 3}
  • .observeDeep(function observer(event){..})
    • Same as .observe, but catches events from all children (if they support .observeDeep)
    • event.path specifies the path of the change event
  • .unobserve(f)
    • Delete an observer

A note on intention preservation

If two users insert something at the same position concurrently, the content that was inserted by the user with the higher user-id will be to the right of the other content. In the OT world we often speak of intention preservation, which is very loosely defined in most cases. This type has the following notion of intention preservation: When a user inserts content c after a set of content C_left, and before a set of content C_right, then C_left will be always to the left of c, and C_right will be always to the right of c. Since content is only marked as deleted (until all conflicts are resolved), this notion of intention preservation is very strong.

A note on time complexities

  • .insert(position, content)
    • O(contents.length)
  • .push(content)
    • O(1)
  • .delete(position, length)
    • O(position + length)
  • .get(i)
    • O(length)
  • Apply a delete operation from another user
    • O(contents.length)
  • Apply an insert operation from another user
    • Yjs does not transform against operations that do not conflict with each other.
    • An operation conflicts with another operation if it intends to be inserted at the same position.
    • Overall worst case complexety: O(|conflicts|^2)



  • Inserting & retrieving types are synchronous operations
    • I.e. `y.share.array.get(0) // => returns a type instead of a promise (if there is a type at position 0)
  • Relies on Yjs@^12.0.0


Yjs is licensed under the MIT License.

kevin.jahns@rwth-aachen.demodel.id[0] === '_'

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