# Check if a string is upper case

Compare a string with its uppercase form.

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

## Implementation

```javascript
function isUpperCase(text) { return text === text.toUpperCase(); }
```

## Input

```json
"SMTP"
```

## Expected output

```json
true
```

## Edge case

Input:
```json
"8812"
```
Output:
```json
true
```

## Limits

- A string without letters is unchanged by toUpperCase, so it counts as upper case, as the edge case shows.

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-string-is-upper-case.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: Curated implementation; explicit input contract, edge case and limits. Original MDX retained as inert source evidence.