> For the complete documentation index, see [llms.txt](https://strctr.gitbook.io/programming/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://strctr.gitbook.io/programming/01-languages/javascript/01-language/c-functions/c4-meta/02-new-proxy.md).

# 02. Create Proxy

Proxies are special objects that allow you customize some of these operations. A proxy is created with two parameters:

* `handler`: For each operation, there is a corresponding handler method that – if present – performs that operation. Such a method intercepts the operation (on its way to the target) and is called a trap (a term borrowed from the domain of operating systems).
* `target`: If the handler doesn’t intercept an operation then it is performed on the target. That is, it acts as a fallback for the handler. In a way, the proxy wraps the target.

If the target is a function, two additional operations can be intercepted:

* `apply`: Making a function call, triggered via
  * proxy(···)
  * proxy.call(···)
  * proxy.apply(···)
* `construct`: Making a constructor call, triggered via `new proxy(···)`

Операции, не соответствующие `handler` автоматически перенаправляются в `target`.

При помощи прокси нельзя перехватить вызов метода. Это нельзя сделать потому, что вызов метода - это одновременно две операции: (1) `get`-получение метода, (2) `apply` вызов функции. Решением является proxy-перехватчик на `get`, который возвращает обработчик перехвата `apply`:

```javascript
function traceMethodCalls(obj) {
  const handler = {
    get(target, propKey, receiver) {
      const origMethod = target[propKey];
      return function(...args) {
        const result = origMethod.apply(this, args);
        console.log(
          propKey + JSON.stringify(args) + " -> " + JSON.stringify(result)
        );
        return result;
      };
    }
  };
  return new Proxy(obj, handler);
}
```