refactor: synchronizer is now 'stateless'

packages/state/synchronizer.js

@@ -4,10 +4,9 @@ import immutablediff from 'immutablediff';
 export class StateSynchronizer {
 
   constructor(statefuls) {
-    this._previousState = I.Map();
     this._state = I.Map();
     this._statefuls = statefuls;
-    this.updateState();
+    this.tick();
   }
 
   acceptStateChange(change) {
@@ -20,27 +19,17 @@ export class StateSynchronizer {
     }
   }
 
-  diff() {
-    const state = this.state();
-    // if (this._previousState === state) {
-    //   return StateSynchronizer.noChange;
-    // }
+  diff(previousState) {
+    const state = this._state;
     const diff = {};
-    let dirty = false;
     for (const key in this._statefuls) {
-      if (this._previousState.get(key) !== state.get(key)) {
+      if (previousState.get(key) !== state.get(key)) {
         diff[key] = this.diffStateful(
-          this._previousState.get(key),
+          previousState.get(key),
           state.get(key)
         );
-        dirty = true;
       }
     }
-    // Side-effect.
-    this._previousState = this.state();
-    if (!dirty) {
-      return StateSynchronizer.noChange;
-    }
     return diff;
   }
 
@@ -73,12 +62,11 @@ export class StateSynchronizer {
     return diff;
   }
 
-  state() {
-    this.updateState();
+  get state() {
     return this._state;
   }
 
-  updateState() {
+  tick() {
     for (const key in this._statefuls) {
       const stateful = this._statefuls[key];
       this._state = this._state.set(key, stateful.state);
@@ -86,5 +74,3 @@ export class StateSynchronizer {
   }
 
 }
-
-StateSynchronizer.noChange = {};