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_posts/2021-9-27-gun-for-react-state-management.md

@@ -12,7 +12,7 @@ image: https://siriusbusiness.fi/assets/images/posts/painless.jpg
 
 Fed up with writing a ton of Redux boilerplate just to make a form input editable?
 
-There’s a better alternative: [Gun.js](https://github.com/amark/gun). It makes state synchronization and persistence super easy.
+There’s a better alternative: [Gun.js](https://github.com/amark/gun). It makes state synchronization and persistence a breeze.
 
 First, initialize Gun with options that make sure the state is synced with localStorage only (not with peers).
 ```jsx
@@ -28,10 +28,8 @@ Then create a React component that uses the state:
 
 ```jsx
 class TextInput extends React.Component {
-    constructor() {
+    state = {text:''};
-        super();
+    
-        this.state = {text:''};
-    }
     componentDidMount() {
         State.get('text').on(text => this.setState({text}));
     }
@@ -53,3 +51,55 @@ class TextInput extends React.Component {
 Now you have a text form that syncs its content across component instances and persists it in localStorage.
 
 See the working example on [Codepen](https://codepen.io/mmalmi/pen/VwWVdKG).
+
+However, if we now unmount the component and write to `State.get('text')` elsewhere, we'll get the warning: `Can't call setState on an unmounted component. This is a no-op, but it indicates a memory leak in your application.`
+
+We can avoid that by saving our state subscriptions and unsubscribing them in `componentWillUnmount()`. Here's a helper class for that:
+
+```jsx
+class BaseComponent extends React.Component {
+    subscriptions = {};
+    
+    subscribe(callback, path) {
+        return (value, key, x, subscription, f) => {
+            if (this.unmounted) {
+                subscription && subscription.off();
+                return;
+            }
+            this.subscriptions[path || key] = subscription;
+            callback(value, key, x, subscription, f);
+        }
+    }
+    
+    inject(name, path) {
+        return this.subscribe((v,k) => {
+            const newState = {};
+            newState[name || k] = v;
+            this.setState(newState);
+        }, path);
+    }
+    
+    componentWillUnmount() {
+        this.unmounted = true;
+        Object.keys(this.subscriptions).forEach(k => {
+            const subscription = this.subscriptions[k];
+            subscription && subscription.off();
+            delete this.subscriptions[k];
+        });
+    }
+}
+```
+
+Now we can extend BaseComponent, which takes care of injecting values to the component's state and unsubscribing on unmount.
+
+```jsx
+class TextInput extends BaseComponent {
+    // ...
+    componentDidMount() {
+        State.get('text').on(this.inject());
+    }
+    // ...
+}
+```
+
+[Codepen](https://codepen.io/mmalmi/pen/MWozPZE)