Chalarangelo/30-seconds-of-code

---
title: You can't extend JavaScript's Proxy object
shortTitle: Extending the Proxy object
type: tip
language: javascript
tags: [object,proxy]
cover: icebreaker
excerpt: Turns out the Proxy object is not extensible, but there's a way around its limitations.
listed: true
dateModified: 2023-04-17
---

While the [`Proxy`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy) object seems like it can be extended by any other class in JavaScript, that's not the case. This is due to proxy objects having very atypical semantics and being considered **exotic objects**. Simply put, this means they do not have a prototype and are not extensible.

So how do you extend a proxy object? You don't. You can, however, create a class that returns a proxy by returning it from the constructor. After all, this is probably the sort of behavior you're after.

```js
class MyProxy {
  constructor(value) {
    Object.keys(value).forEach(key => (this[key] = value[key]));
    return new Proxy(this, {
      set(object, key, value) {
        console.log(`Called with ${key} = ${value}`);
        object[key] = value;
        return true;
      }
    });
  }
}

const myProxy = new MyProxy({ a: 1 });
myProxy.b = 2; // LOGS: 'Called with b = 2'
```