# Check if a number is a power of 2

Use the bit trick n & (n − 1) on a positive integer.

Canonical: https://1loc.dev/validator/check-if-a-number-is-a-power-of-2/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function isPowerOfTwo(n) { return n > 0 && (n & (n - 1)) === 0; }
```

## Input

```json
64
```

## Expected output

```json
true
```

## Edge case

Input:
```json
0
```
Output:
```json
false
```

## Limits

- The original returned true for 0; this version requires n > 0.
- Bitwise operators use 32-bit integers, so the lab accepts 0 to 2^30.

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-number-is-a-power-of-2.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: Requires n > 0; the original returned true for 0. Original MDX retained as inert source evidence.