# Check if a value is a plain object

Return true for objects whose prototype is Object.prototype or null.

Canonical: https://1loc.dev/validator/check-if-a-value-is-a-plain-object/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function isPlainObject(value) { return value !== null && typeof value === 'object' && [null, Object.prototype].includes(Object.getPrototypeOf(value)); }
```

## Input

```json
{
  "a": 1
}
```

## Expected output

```json
true
```

## Edge case

Input:
```json
[]
```
Output:
```json
false
```

## Limits

- Uses Object.getPrototypeOf instead of the __proto__ accessor, which an own "__proto__" key can shadow.
- JSON cannot create class instances; in code, instances of classes return false.

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/check-if-a-value-is-a-plain-object.mdx
Source file (this edition): https://github.com/akamind/1loc/blob/0a77f131b22d2ba3b7ec1728846f900c22821678/contents/check-if-a-value-is-a-plain-object.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Uses Object.getPrototypeOf instead of the __proto__ accessor. Original MDX retained as inert source evidence.