Dummu - Concurrency in Regex

This works perfectly in every manual test and falls apart the moment two things happen at once.

Why this matters for Regex

This is a bold claim, an italic aside, and an underlined point, all in one Regex example.

What it touches:

• The Regex runtime or interpreter
• Whatever calls the code around it
• Anyone reading this six months from now

How to apply it:

1. Read the snippet below once, slowly.
2. Try changing one value and predict the output before running it.
3. Compare your prediction against what actually happens.

"Concurrency bugs hide until load exposes them, so reason about the ordering explicitly."

'2026-08-26'.match(/^(\d{4})-(\d{2})-(\d{2})$/);
// ['2026-08-26', '2026', '08', '26']

Reference: Regex documentation

Concurrency bugs hide until load exposes them, so reason about the ordering explicitly.