Add JS immutable proxy

blog_posts/js-immutable-object-proxy.md

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+---
+title: Immutable JavaScript objects using the Proxy object
+type: story
+tags: javascript,object,proxy
+expertise: advanced
+author: chalarangelo
+cover: blog_images/frozen-globe.jpg
+excerpt: Freezing objects is not the only way to prevent mutations. Learn how you can leverage the Proxy object to your advantage.
+firstSeen: 2022-04-10T05:00:00-04:00
+---
+
+Object mutability and its relation to the `const` keyword is a very common headache for developers. More often than not, when looking for ways to make an object immutable, `Object.freeze()` will pop up as a solution. We’ve explored this approach previously, elaborating on deep freezing solutions. You can read more about it in [this article](/articles/s/javascript-deep-freeze-object).
+
+While `Object.freeze()` is the more straightforward approach, it might not always be the best solution. This may be especially true when dealing with extensive object nesting or when objects have a very short life. For such cases, a different approach using the [Proxy object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy) might make more sense. Here’s what that looks like:
+
+```js
+const term = {
+  id: 1,
+  value: 'hello',
+  properties: [{ type: 'usage', value: 'greeting' }],
+};
+
+const immutable = obj =>
+  new Proxy(obj, {
+    get(target, prop) {
+      return typeof target[prop] === 'object'
+        ? immutable(target[prop])
+        : target[prop];
+    },
+    set() {
+      throw new Error('This object is immutable.');
+    },
+  });
+
+const immutableTerm = immutable(term);
+const immutableProperty = immutableTerm.properties[0];
+
+immutableTerm.name = 'hi';            // Error: This object is immutable.
+immutableTerm.id = 2;                 // Error: This object is immutable.
+immutableProperty.value = 'pronoun';  // Error: This object is immutable.
+```
+
+Even though proxies are not all that common, this code shouldn’t be hard to understand. The gist of the idea is that you use a handler to prevent mutations to the object via the `set()` trap. Additionally, you use the `get()` trap to enforce immutability on all nested values. This is done by checking the type of the value and applying the proxy to nested objects.
+
+That’s pretty much all there is to it. With just a few lines of code, you now have a way to prevent mutation on an object, regardless of shape, nesting or complexity.