npm / re2js

re2js

What changed in re2js 1 to 2, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-17.

2 breaking4 security12 new APIs and options6 performance4 behavior and defaults1 tooling19 fixes and other

See which of these apply to your code, ranked, in your agent:

npx @unstale/cli init

re2js 239 changes

Pass true for the new javaMode flag to opt into the previous Java-style escaping and invalid capture group exceptions.
2.0.0release notes
replaceAll and replaceFirst now use native ECMAScript replacement semantics by default: $$ escapes a dollar sign, and backslash is treated literally.
2.0.0release notes

Adds a new exec method.
2.8.5release notes
RE2Set now supports customizing its memory limit.
2.8.3release notes
Supports more Unicode categories, including Emoji, Emoji_Component, Emoji_Modifier, and ASCII_Hex_Digit.
2.8.2release notes
replaceAll() now accepts a function as replacement in addition to a string.
2.8.0release notes
replaceFirst() now accepts a function as replacement in addition to a string.
2.8.0release notes
Added the matchAll method.
2.6.0release notes
Added a tagged template literal method for constructing regular expressions.
2.5.0release notes
RE2 lookbehinds are supported.
2.2.0release notes

Fixes quadratic-time behavior when LOOKBEHINDS is used with repeated-matching APIs such as matcher().find() in a loop, matchAll(), split(), and matcher().replaceAll().
2.8.7release notes
Removes O(n) array copying during UTF-8 encoding.
2.8.6release notes
Optimizes the per-byte spawning loop for the LOOKBEHINDS flag.
2.7.1release notes
Word boundaries are faster.
2.3.2release notes
Added an Aho-Corasick prefilter.
2.2.1release notes
Performance improvements for DFA may improve regular expression execution speed.
2.0.1release notes

Fixes bugs in replace.
2.8.6release notes
Fixes bugs in split.
2.8.6release notes
Fixes the types for resetMatcherInput.
2.8.5release notes
Fixes polymorphic inputs to resetMatcherInput.
2.8.4release notes
Fixes TypeScript types for more methods.
2.8.1release notes
Adds AST SyntaxError validation for the LOOKBEHINDS flag, helping identify invalid syntax.
2.7.0release notes
Fixed a desynchronization bug in matchAll.
2.6.1release notes
Fixes Unicode case folding across all JavaScript environments.
2.4.0release notes
Fixes were made to the TypeScript declaration files.
2.3.1release notes
TypeScript type fixes were made.
2.3.0release notes
Fixes were made to translateRegExp().
2.2.3release notes
Unicode fixes may change how regular expressions handle Unicode.
2.2.3release notes
Fixes issues that cause “Maximum call stack size exceeded.”
2.2.2release notes
Fixed a compiler memory leak.
2.2.1release notes
Fixed onepass logic.
2.2.1release notes
Zero-width matches no longer corrupt UTF-8 or UTF-16.
2.2.1release notes
The RE2Set flags interface is fixed.
2.2.0release notes

Fixes information disclosure and XSS in Matcher.quoteReplacement.
1.3.3release notes
Instance and static matches() methods use the testExact() DFA fast-path, providing a significant performance boost and ReDoS immunity.
1.3.2release notes

Adds high-performance boolean testing with test(), offering a faster alternative to matcher.find() for checking whether a pattern matches.
1.3.1release notes
Adds a high-performance boolean testing method for exact matching.
1.3.1release notes
Introduced lazy DFA.
1.3.0release notes
Adds a Matcher export for TypeScript consumers.
1.2.3release notes