Work

On the computational complexity of JavaScript regex matching

Year: 2026

Type: preprint

Abstract: Despite widespread use, the complexity of the matching problem for modern regular expressions languages remains unclear. Previous work proved that an idealized regular expression language with backreferences and lookarounds had PSPACE-complete matching. We extend this work to a real-world regex language by proving that JavaScript regex matching with expanded lower-bounded quantifiers is PSPACE-complete. We then generalize the result: we show that PSPACE-hardness survives the removal of negative lookarounds, and that removing all lookarounds leads to an OptP-complete parsing problem. Our core arguments are formalized in Rocq.

Source: arXiv (Cornell University)

DOI: 10.48550/arxiv.2603.26139

Authors: Deng, Victor, Barrière, Aurèle, Pit-Claudel, Clément

Institutions: Lyon 1 Université, École Normale Supérieure de Lyon, Centre National de la Recherche Scientifique, Institut national de recherche en sciences et technologies du numérique, École Polytechnique Fédérale de Lausanne

Topic: semigroups and automata theory

Subfield: Computational Theory and Mathematics

Field: Computer Science

Domain: Physical Sciences

Open Access status: green

Funders: National Science Foundation, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung

Award: ReSET: Regex matching made Safe, Effective, and Trustworthy

OpenAlex ID: W7143431861

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