# Check if a string consists of a repeated character sequence

Find the string inside itself doubled, past the first position.

Canonical: https://1loc.dev/string/check-if-a-string-consists-of-a-repeated-character-sequence/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function consistsRepeatedSubstring(text) { return `${text}${text}`.indexOf(text, 1) !== text.length; }
```

## Input

```json
"abcabc"
```

## Expected output

```json
true
```

## Edge case

Input:
```json
"abcab"
```
Output:
```json
false
```

## Limits

- The empty string returns false. Comparison is by UTF-16 code units.

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-consists-of-a-repeated-character-sequence.mdx
Source file (this edition): https://github.com/akamind/1loc/blob/0a77f131b22d2ba3b7ec1728846f900c22821678/contents/check-if-a-string-consists-of-a-repeated-character-sequence.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.