The Blackboard is the memory structure required by BehaviorTree and its nodes. It only have 2 public methods: set and get. These methods works in 3 different contexts: global, per tree, and per node per tree.

Suppose you have two different trees controlling a single object with a single blackboard, then:

• In the global context, all nodes will access the stored information.
• In per tree context, only nodes sharing the same tree share the stored information.
• In per node per tree context, the information stored in the blackboard can only be accessed by the same node that wrote the data.

The context is selected indirectly by the parameters provided to these methods, for example:

// getting/setting variable in global context
blackboard.set('testKey', 'value');
var value = blackboard.get('testKey');

// getting/setting variable in per tree context
blackboard.set('testKey', 'value', tree.id);
var value = blackboard.get('testKey', tree.id);

// getting/setting variable in per node per tree context
blackboard.set('testKey', 'value', tree.id, node.id);
var value = blackboard.get('testKey', tree.id, node.id);

Note: Internally, the blackboard store these memories in different objects, being the global on _baseMemory, the per tree on _treeMemory and the per node per tree dynamically create inside the per tree memory (it is accessed via _treeMemory[id].nodeMemory). Avoid to use these variables manually, use get and set instead.