List Type for Yjs

Manage list-like data with this shareable list type. You can insert and delete arbitrary objects (also custom types for Yjs) in the list type.

Use it!

Retrieve this with bower or npm.

Bower

bower install y-list --save

and include the js library.

<script src="./bower_components/y-list/y-list.js"></script>

NPM

npm install y-list --save

and put it on the Y object.

Y.List = require("y-list");

List Object

Reference

• Create

var ylist = new Y.List()

• .insert(position, content)
  • Insert content at a position
• .insertContents(position, contents)
  • Insert a set of content at a position. This expects that contents is an array of content.
• .push(content)
  • Insert content at the end of the list
• .delete(position, length)
  • Delete content. The length parameter is optional and defaults to 1
• .val()
  • Retrieve all content as an Array Object
• .val(position)
  • Retrieve content from a position
• .ref(position)
  • Retrieve a reference to the element on a position.
  • You can call ref.getNext() and ref.getPrev() to get the next/previous reference
  • You can call ref.getNext(i) and ref.getPrev(i) to get the i-th next/previous reference
  • You can call ref.val() to get the element, to which the reference points (y.ref(1).val() === y.val(1))
• .observe(f)
  • The observer is called whenever something on this list changed. (throws insert, and delete events)
• .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. This property will also hold when content is deleted or when a deletion is undone.

A note on time complexities

• .insert(position, content)
  • O(position)
• .insertContents(position, contents)
  • O(position + |contents|)
• .push(content)
  • O(1)
• .delete(position, length)
  • O(position)
• .val()
  • O(|ylist|)
• .val(position)
  • O(position|)
• Apply a delete operation from another user
  • O(1)
• 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|!)

Issues

• Support moving of objects
• Create a polymer element

License

Yjs is licensed under the MIT License.

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