Check if a string consists of a repeated character sequence

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

JavaScript Version 1.0.0 · MIT · .md

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

Input & expected output

"abcabc"

true

The edge case

"abcab"

false

Know the limits

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

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Capitalize a string — Uppercase the first Unicode code point and preserve the remaining text.
• Reverse a string — Reverse Unicode code points without splitting surrogate pairs.
• Check a palindrome — Compare a string with its code-point reversal.