#

Yjs is a framework for offline-first p2p shared editing on structured data like text, richtext, json, or XML. It is fairly easy to get started, as Yjs hides most of the complexity of concurrent editing. For additional information, demos, and tutorials visit y-js.org.

### Extensions

Yjs only knows how to resolve conflicts on shared data. You have to choose a ..

- Connector - a communication protocol that propagates changes to the clients
- Database - a database to store your changes
- one or more Types - that represent the shared data

Connectors, Databases, and Types are available as modules that extend Yjs. Here is a list of the modules we know of:

##### Connectors

Name | Description
--- | ---
webrtc | Propagate updates Browser2Browser via WebRTC
websockets | Set up a central server, and connect to it via websockets
xmpp | Propagate updates in a XMPP multi-user-chat room (XEP-0045)
ipfs | Connector for the Interplanetary File System!
test | A Connector for testing purposes. It is designed to simulate delays that happen in worst case scenarios

##### Database adapters

Name | Description
--- | ---
memory | In-memory storage.
indexeddb | Offline storage for the browser
leveldb | Persistent storage for node apps

##### Types

Name | Description
--- | ---
map | A shared Map implementation. Maps from text to any stringify-able object
array | A shared Array implementation
xml | An implementation of the DOM. You can create a two way binding to Browser DOM objects
text | Collaborate on text. Supports two way binding to the Ace Editor, CodeMirror, Monaco, textareas, input elements, and HTML elements (e.g. <h1>, or <p>)
richtext | Collaborate on rich text. Supports two way binding to the Quill Rich Text Editor

##### Other

Name | Description
--- | ---
y-element | Yjs Polymer Element

## Use it!

Install Yjs, and its modules with bower, or npm.

### Bower

    bower install --save yjs y-array % add all y-* modules you want to use

You only need to include the `y.js` file. Yjs is able to automatically require missing modules.

    <script src="./bower_components/yjs/y.js"></script>

### CDN

    <script src="https://cdn.jsdelivr.net/npm/yjs@12/src/y.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/y-array@10/dist/y-array.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/y-websockets-client@8/dist/y-websockets-client.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/y-memory@8/dist/y-memory.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/y-array@10/dist/y-array.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/y-map@10/dist/y-map.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/y-text@9/dist/y-text.js"></script>
    // ..
    // do the same for all modules you want to use

### Npm

    npm install --save yjs % add all y-* modules you want to use

If you don't include via script tag, you have to explicitly include all modules! (Same goes for other module systems)

    var Y = require('yjs')
    require('y-array')(Y) // add the y-array type to Yjs
    require('y-websockets-client')(Y)
    require('y-memory')(Y)
    require('y-array')(Y)
    require('y-map')(Y)
    require('y-text')(Y)
    // ..
    // do the same for all modules you want to use

### ES6 Syntax

    import Y from 'yjs'
    import yArray from 'y-array'
    import yWebsocketsClient from 'y-webrtc'
    import yMemory from 'y-memory'
    import yArray from 'y-array'
    import yMap from 'y-map'
    import yText from 'y-text'
    // ..
    Y.extend(yArray, yWebsocketsClient, yMemory, yArray, yMap, yText /*, .. */)

# Text editing example

Install dependencies

    bower i yjs y-memory y-webrtc y-array y-text

Here is a simple example of a shared textarea

      <!DOCTYPE html>
      <html>
        <body>
          <script src="./bower_components/yjs/y.js"></script>
          <!-- Yjs automatically includes all missing dependencies (browser only) -->
          <script>
            Y({
              db: {
                name: 'memory' // use memory database adapter.
                // name: 'indexeddb' // use indexeddb database adapter instead for offline apps
              },
              connector: {
                name: 'webrtc', // use webrtc connector
                // name: 'websockets-client'
                // name: 'xmpp'
                room: 'my-room' // clients connecting to the same room share data
              },
              sourceDir: '/bower_components', // location of the y-* modules (browser only)
              share: {
                textarea: 'Text' // y.share.textarea is of type y-text
              }
            }).then(function (y) {
              // The Yjs instance `y` is available
              // y.share.* contains the shared types

              // Bind `y.share.textarea` to `<textarea/>`
              y.share.textarea.bind(document.querySelector('textarea'))
            })
          </script>
          <textarea></textarea>
        </body>
      </html>

## Get Help & Give Help

There are some friendly people on who are eager to help, and answer questions. Please join!

Report any issues to the Github issue page! I try to fix them very soon, if possible.

# API

### Y(options)

- Y.extend(module1, module2, ..)
  - Add extensions to Y
  - `Y.extend(require('y-webrtc'))` has the same semantics as `require('y-webrtc')(Y)`
- options.db
  - Will be forwarded to the database adapter. Specify the database adaper on `options.db.name`.
  - Have a look at the used database adapter repository to see all available options.
- options.connector
  - Will be forwarded to the connector adapter. Specify the connector adaper on `options.connector.name`.
  - All our connectors implement a `room` property. Clients that specify the same room share the same data.
  - All of our connectors specify an `url` property that defines the connection endpoint of the used connector.
    - All of our connectors also have a default connection endpoint that you can use for development.
  - Set `options.connector.generateUserId = true` in order to genenerate a userid, instead of receiving one from the server. This way the `Y(..)` is immediately going to be resolved, without waiting for any confirmation from the server. Use with caution.
  - Have a look at the used connector repository to see all available options.
  - Only if you know what you are doing: Set `options.connector.preferUntransformed = true` in order receive the shared data untransformed. This is very efficient as the database content is simply copied to this client. This does only work if this client receives content from only one client.
- options.sourceDir (browser only)
  - Path where all y-* modules are stored
  - Defaults to `/bower_components`
  - Not required when running on `nodejs` / `iojs`
  - When using nodejs you need to manually extend Yjs:

        var Y = require('yjs')
        // you have to require a db, connector, and *all* types you use!
        require('y-memory')(Y)
        require('y-webrtc')(Y)
        require('y-map')(Y)
        // ..

- options.share
  - Specify on `options.share[arbitraryName]` types that are shared among all users.
  - E.g. Specify `options.share[arbitraryName] = 'Array'` to require y-array and create an y-array type on `y.share[arbitraryName]`.
  - If userA doesn't specify `options.share[arbitraryName]`, it won't be available for userA.
  - If userB specifies `options.share[arbitraryName]`, it still won't be available for userA. But all the updates are send from userB to userA.
  - In contrast to y-map, types on `y.share.*` cannot be overwritten or deleted. Instead, they are merged among all users. This feature is only available on `y.share.*`
  - Weird behavior: It is supported that two users specify different types with the same property name. E.g. userA specifies `options.share.x = 'Array'`, and userB specifies `options.share.x = 'Text'`. But they only share data if they specified the same type with the same property name
- options.type (browser only)
  - Array of modules that Yjs needs to require, before instantiating a shared type.
  - By default Yjs requires the specified database adapter, the specified connector, and all modules that are used in `options.share.*`
  - Put all types here that you intend to use, but are not used in y.share.*

### Instantiated Y object (y)

`Y(options)` returns a promise that is fulfilled when..

- All modules are loaded
  - The specified database adapter is loaded
  - The specified connector is loaded
  - All types are included
- The connector is initialized, and a unique user id is set (received from the server)
  - Note: When using y-indexeddb, a retrieved user id is stored on `localStorage`

The promise returns an instance of Y. We denote it with a lower case `y`.

- y.share.*
  - Instances of the types you specified on options.share.*
  - y.share.* can only be defined once when you instantiate Y!
- y.connector is an instance of Y.AbstractConnector
- y.connector.onUserEvent(function (event) {..})
  - Observe user events (event.action is either 'userLeft' or 'userJoined')
- y.connector.whenSynced(listener)
  - `listener` is executed when y synced with at least one user.
  - `listener` is not called when no other user is in the same room.
  - y-websockets-client aways waits to sync with the server
- y.connector.disconnect()
  - Force to disconnect this instance from the other instances
- y.connector.reconnect()
  - Try to reconnect to the other instances (needs to be supported by the connector)
  - Not supported by y-xmpp
- y.close()
  - Destroy this object.
  - Destroys all types (they will throw weird errors if you still use them)
  - Disconnects from the other instances (via connector)
  - Returns a promise
- y.destroy()
  - calls y.close()
  - Removes all data from the database
  - Returns a promise
- y.db.stopGarbageCollector()
  - Stop the garbage collector. Call y.db.garbageCollect() to continue garbage collection
- y.db.gc :: Boolean
  - Whether gc is turned on
- y.db.gcTimeout :: Number (defaults to 50000 ms)
  - Time interval between two garbage collect cycles
  - It is required that all instances exchanged all messages after two garbage collect cycles (after 100000 ms per default)
- y.db.userId :: String
  - The used user id for this client. Never overwrite this

### Logging

Yjs uses debug for logging. The flag `y*` enables logging for all y- components. You can selectively remove components you are not interested in: E.g. The flag `y,-y:connector-message`will not log the long`y:connector-message` messages.

##### Enable logging in Node.js

    DEBUG=y* node app.js

Remove the colors in order to log to a file:

    DEBUG_COLORS=0 DEBUG=y* node app.js > log

##### Enable logging in the browser

    localStorage.debug = 'y*'

## Contribution

I created this framework during my bachelor thesis at the chair of computer science 5 (i5), RWTH University. Since December 2014 I'm working on Yjs as a part of my student worker job at the i5.

## License

Yjs is licensed under the MIT License.

yjs@dbis.rwth-aachen.de