> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lilbots.io/llms.txt
> Use this file to discover all available pages before exploring further.

# JavaScript Runtime Gotchas

> This document covers some edge cases and gotchas with the javascript runtime.

## `__proto__` property of objects:

The Deno runtime does not support the `__proto__` property of objects. This is a deprecated feature of the JavaScript language and should not be used in modern code. Instead, use `Object.getPrototypeOf` and `Object.setPrototypeOf` to get and set the prototype of an object. The following discussion on Deno's GitHub elaborates: [https://github.com/denoland/deno/issues/4324](https://github.com/denoland/deno/issues/4324).

However because Node still supports `__proto__` many NPM libraries still use `__proto__` and will break in Deno. To fix this, you can add the following code to the top of your program:

```javascript theme={null}
Object.defineProperty(Object.prototype, '__proto__', {
    get: function() {
        return Object.getPrototypeOf(this);
    }
})
```

As the `__proto__` is non-standard in Deno and poses a security risk, we have chosen not to add this workaround to the runtime by default, but rather let developers add it ad-hoc to their programs. We hope libraries will migrate away from using `__proto__` in the future.

## `process.versions` missing:

In node js, you can access the version of the node runtime using `process.versions`. This is not available in Deno by default - meaning that NPM libraries that rely on this will break in Deno. This can manifest as an error like `Cannot read property 'node' of undefined`.

To fix this, you can add the following code to the top of your program:

```javascript theme={null}
import { versions } from 'node:process';
process.versions = versions
```

Reference: [https://docs.deno.com/api/node/process/\~/Process.versions](https://docs.deno.com/api/node/process/~/Process.versions)