add code ya know

interactor.js

@@ -0,0 +1,52 @@
+import { Stream } from './stream.js';
+
+export class Interactor {
+  _actions = new Stream();
+  _reactions = new Stream();
+  _latestReaction;
+
+  constructor(initialReaction = new Reaction()) {
+    this._latestReactions = {};
+    this._actions.listen((action) => this._interaction(action));
+    this._react(initialReaction);
+  }
+
+  act(action) {
+    if (!(action instanceof Action)) throw 'invalid action';
+    this._actions.add(action);
+  }
+
+  observe(reactionHandler, provideLatestReaction = true) {
+    if (provideLatestReaction) reactionHandler(this._latestReaction);
+    let listener = (reaction) => {
+      if (!(reaction instanceof Reaction)) throw 'invalid reaction';
+      reactionHandler(reaction);
+    };
+    this._reactions.listen(listener);
+    return listener;
+  }
+
+  ignore(listener) {
+    this._reactions.ignore(listener);
+  }
+
+  _interaction(action) {}
+
+  _react(reaction) {
+    if (!(reaction instanceof Reaction)) throw 'invalid reaction';
+    let latest = this._latestReactions[reaction.constructor.name];
+    if (!reaction.equals(latest)) {
+      this._latestReaction = reaction;
+      this._latestReactions[reaction.constructor.name] = reaction;
+      this._reactions.add(reaction);
+    }
+  }
+}
+
+export class Action {}
+
+export class Reaction {
+  equals(reaction) {
+    return false;
+  }
+}