Regular Expression \R Escape for ECMAScript

Status

Stage: 1
Champion: Ron Buckton (@rbuckton)

For detailed status of this proposal see TODO, below.

Authors

• Ron Buckton (@rbuckton)

Motivations

NOTE: See https://github.com/rbuckton/proposal-regexp-features for an overview of how this proposal fits into other possible future features for Regular Expressions.

The \R escape sequence matches the various sets of code points that match a unicode line terminator, which can be difficult to write correctly.

Prior Art

• Perl
• PCRE
• Boost.Regex
• Oniguruma
• ICU
• Glib/GRegex

See https://rbuckton.github.io/regexp-features/features/line-endings-escape.html for additional information.

Syntax

• \R — Matches any line ending character sequence.

NOTE: Requires the u or v flags, as \R is currently just an escape for R without the u flag.

NOTE: Not supported inside of a character class.

Semantics

• In u or v mode, \R is roughly equivalent to the following pattern:

  (?>\r\n?|[\x0A-\x0C\x85\u{2028}\u{2029}])

  • Aligns with ^ and $ in mu mode
• When not in u or v mode, \R will continue to match the literal character R.

NOTE: The above example uses atomic groups (?>) to prevent backtracking when matching \r\n?. Atomic groups is proposed here.

Examples

// split lines regardless of line termiantor style
const lines = fs.readFileSync("file.txt", "utf8").split(/\R/ug);

History

• October 28, 2021 — Proposed for Stage 1 (slides)
  • Outcome: Advanced to Stage 1

TODO

The following is a high-level list of tasks to progress through each stage of the TC39 proposal process:

Stage 1 Entrance Criteria

• Identified a "champion" who will advance the addition.
• Prose outlining the problem or need and the general shape of a solution.
• Illustrative examples of usage.
• High-level API.

Stage 2 Entrance Criteria

• Initial specification text.
• Transpiler support (Optional).

Stage 3 Entrance Criteria

• Complete specification text.
• Designated reviewers have signed off on the current spec text.
• The ECMAScript editor has signed off on the current spec text.

Stage 4 Entrance Criteria

• Test262 acceptance tests have been written for mainline usage scenarios and merged.
• Two compatible implementations which pass the acceptance tests: [1], [2].
• A pull request has been sent to tc39/ecma262 with the integrated spec text.
• The ECMAScript editor has signed off on the pull request.