fix: Handle errors thrown from updates.

src/index.ts

@@ -21,6 +21,10 @@ export class ImmutableModelStore<S> {
         this.current = produce(initialState, () => void 0) as Immutable<S>;
     }
 
+    public get updating(): boolean {
+        return !!this._isUpdating;
+    }
+
     /**
      * update() will synchronously update the state of the model.
      *
@@ -35,22 +39,26 @@ export class ImmutableModelStore<S> {
         } else {
             const draft = (this._isUpdating = createDraft(this.current) as Draft<S>);
 
-            // Apply the update...
-            const voidResult = fn(draft) as any;
+            try {
+                // Apply the update...
+                const voidResult = fn(draft) as any;
 
-            // Paranoid check for async functions...
-            if (typeof voidResult === 'object' && 'then' in voidResult) {
-                throw new Error('Updates must be synchronous');
-            }
+                // Paranoid check for async functions...
+                if (typeof voidResult === 'object' && 'then' in voidResult) {
+                    throw new Error('Updates must be synchronous');
+                }
 
-            const newState = finishDraft(draft) as Immutable<S>;
+                const newState = finishDraft(draft) as Immutable<S>;
 
-            this._isUpdating = undefined;
-            if (newState !== this.current) {
-                this.current = newState;
+                this._isUpdating = undefined;
+                if (newState !== this.current) {
+                    this.current = newState;
 
-                // Notify subscribers.
-                this._subscribers.forEach((subscriber) => subscriber(this.current));
+                    // Notify subscribers.
+                    this._subscribers.forEach((subscriber) => subscriber(this.current));
+                }
+            } finally {
+                this._isUpdating = undefined;
             }
         }
     }

test/ImmutableModelStoreTest.ts

@@ -83,4 +83,21 @@ describe('ImmutableModelStore', () => {
         });
         expect(listener).to.have.beenCalledTimes(1);
     });
+
+    it('should handle an exception from update', () => {
+        const store = new ImmutableModelStore({ name: 'Jason', age: 30 });
+
+        expect(() =>
+            store.update((state) => {
+                state.age = 31;
+                throw new Error('boom');
+            })
+        ).to.throw('boom');
+
+        // Update should not have been applied.
+        expect(store.current.age).to.equal(30);
+
+        // We should not be in the middle of a re-rentrant update.
+        expect(store.updating).to.be.false;
+    });
 });