observed-remove-map

An "Observed-Remove Map" or "OR-Map", is a Map data type that can be modified concurrently and will eventually reach the same state everywhere (it is "eventually consistent").

Built with observed-remove-set.

example

var map1 = new OrMap('bob')
var map2 = new OrMap('alice')
 
// let's provide a "delay" function to simulate concurrency on a network
function delay (cb) {
  setTimeout(cb, 3000) // 3 seconds of delay!
}
 
// let's "connect" our two maps
map1.on('op', op => delay(() => map2.receive(op)))
map2.on('op', op => delay(() => map1.receive(op)))
 
// both Bob and Alice simulatenously set "a" to different values
map1.set('a', 0) // {a:0}
map2.set('a', 1) // {a:1}

In a normal Map type, this would cause a conflict! However, these are Or-Maps and will handle conflicts for us. Once all operations have been delivered, both Bob and Alice are guaranteed to have the same data.

// after all operations have been received...
map1.get('a') // 0
map2.get('a') // 0

install

npm install observed-remove-map

<script src="dist/or-map.js"></script>

api

orMap = new OrMap(uuid, [opts])

Create a new OR-Map.

Required uuid is some universally unique identifer for this map.

Optional opts object is an object of the form:

{
  serialize: (Object) => {},              // custom object serializer
  parse: (String) => {},                  // custom object deserializer
  compareKeys: (Object, Object) => bool,  // custom key comparator (returns true if objects are equal)
  compareValues(Object, Object) => bool   // custom value comparator
}

orMap.add(key)

Add a key to the map with a value of null.

element is any serializable Javascript object. Changes to within this object will NOT be replicated.

orMap.delete(key)

Remove a key and it's value from the map.

orMap.set(key, value)

Sets the value at key. If key does not exist, it will be added first.

orMap.has(key)

Returns true if the map contains the given key.

orMap.get(key)

Returns the value associated with the given key.

orMap.keys()

Returns an array with all keys.

orMap.values()

Returns an array with all values.

orMap.receive(op)

Receive an operation from a remote map. Must be called exactly once per remote operation.

orMap.getState()

Get the complete state of the system. Useful for complete replication to other sites. Not consistency safe without a 2-step sync.

orMap.setState(sate)

Set the complete state of the system (use the state object from getState). Useful for complete replication to other sites. Not consistency safe without a 2-step sync.

orMap.on('op', function (op) {})

Fires when an operation needs to be sent to connected Maps. Operations can be delivered in any order and more-than-once, but must be delivered at-least-once. There may be multiple operation events for each call to a method.

op is the operation object that needs to be passed into otherOrMap.receive(op) for all other replicas.

orMap.on('add', function (key) {})

Fires when a new key is added to the map by a remote operation. (will not fire when orMap.add() is called locally.)

orMap.on('delete', function (key) {})

Fires when a key is removed from the map by a remote operation. (will not fire when orMap.delete() is called locally.)

orMap.on('set', function (key, value) {})

Fires when the value associated with a key is changed by a remote operation. (will not fire when orMap.set() is called locally.)