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The option shipped in 1.4.0 and is declared in bun-types, but the stringWidth section of docs/runtime/utils.mdx (including its inlined options type) did not mention it. Add it to the example block, the prose and the inlined definition, mirroring the JSDoc in bun.d.ts. Also pin the documented values in stringWidth.test.ts: the option is off by default, counts each member of an emoji sequence, follows node's per-code-point widths, and composes with countAnsiEscapeCodes and ambiguousIsNarrow on both the Latin-1 and UTF-16 paths.
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Updated 6:05 AM PT - Aug 14th, 2026
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Status: ready for review (head 67930da).
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WalkthroughThe pull request documents the ChangesString width per-code-point support
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Inline comments:
In `@docs/runtime/utils.mdx`:
- Around line 329-333: Update the string-width documentation to limit
compatibility to the default behavior, and explicitly identify perCodePoint as a
Bun-specific option. Clarify that code using perCodePoint cannot be ported
unchanged to string-width.
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docs/runtime/utils.mdxtest/js/bun/util/stringWidth.test.ts
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LGTM — docs-and-tests only, no runtime changes.
What was reviewed:
- The new
perCodePointJSDoc block inutils.mdxmatchespackages/bun-types/bun.d.tsverbatim, and the prose/example values (2 vs 8 for the family emoji) match the implementation insrc/jsc/bindings/stringWidth.cpp. - Traced each pinned test value (flag 4, skin-tone modifier 4, rainbow flag 3, keycap 1, soft hyphen 3, ambiguous-wide soft hyphen 4,
countAnsiEscapeCodescomposition 12/10/15) throughperCodePointColumnWidth— all correct. - The prototype-pollution test addition matches how
stringWidth.cppreads the option viagetIfPropertyExistsPrototypePollutionMitigation, and thefinallycleanup is symmetric.
Extended reasoning...
Overview
This PR documents the perCodePoint option of Bun.stringWidth (shipped in 1.4.0 via #34660 but never documented) and adds test coverage for it. Two files touched: docs/runtime/utils.mdx (two example lines, one prose paragraph, and the option added to the inlined TypeScript definition block) and test/js/bun/util/stringWidth.test.ts (a new describe("perCodePoint") block plus three lines added to the existing prototype-pollution test). No runtime code is changed.
Security risks
None. This is prose documentation plus test assertions against an already-shipped API. No new code paths, no input handling, no auth/crypto/permissions surface.
Level of scrutiny
Low. Docs changes need to be checked for accuracy against the implementation, and test additions need to be checked for correctness of the pinned values so they don't lock in wrong behavior. I verified both:
- The JSDoc block added to
utils.mdxis byte-identical to the existingpackages/bun-types/bun.d.tsentry (lines 561-569), so the two definitions cannot drift apart in this PR. - I read
perCodePointColumnWidthinsrc/jsc/bindings/stringWidth.cppand manually computed each pinned value: family emoji = 4×2 + 3×0 = 8; regional-indicator flag = 2+2 = 4; thumbs-up + skin tone = 2+2 (skin-tone modifiers are EAW=Wide, so the switch returns 2 before reaching the Emoji_Modifier zero-width check); rainbow flag = 1+0+0+2 = 3 (U+1F3F3 is EAW=Neutral without Emoji_Presentation); keycap = 1+0+0 = 1; soft hyphen = 1 per node's special case, and 2 underambiguousIsNarrow: falsesince U+00AD is EAW=Ambiguous; thecountAnsiEscapeCodescompositions (12/10/15) follow from ESC/C1 being Cc → 0 with the printable escape bytes counted individually. Every asserted number is correct. - The prototype-pollution test addition is symmetric (set in
try, delete infinally) and matches how the option is read viagetIfPropertyExistsPrototypePollutionMitigationinstringWidth.cpp:1136.
Other factors
The PR description explicitly scopes out the stale ambiguousIsNarrow JSDoc in the same block (handled by #30696), which is the right call — it keeps this PR focused and the two apply cleanly together. The new tests use exact .toBe/.toEqual assertions (no snapshots, no vacuous checks), cover both the Latin-1 and UTF-16 code paths, and compose the option with both other options. The author states 179 tests pass on bun bd test, and since the runtime is unchanged the tests pin existing behavior rather than proving a fix — that's fine for a docs PR.
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Review follow-up, as of 67930da:
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LGTM — docs-only addition plus tests pinning already-shipped behavior.
What was reviewed:
- Confirmed the inlined JSDoc block matches
packages/bun-types/bun.d.tsverbatim and the option is parsed insrc/jsc/bindings/stringWidth.cppwith defaultfalseviagetIfPropertyExistsPrototypePollutionMitigation. - Spot-checked the new test values (family emoji = 8, rainbow flag = 3, keycap = 1, soft hyphen = 1 column, ANSI/C1 composition counts) against
perCodePointColumnWidth— all trace correctly through the EAW → Emoji_Presentation → zero-width-category logic on both the Latin-1 and UTF-16 paths. - CodeRabbit's
string-widthcompatibility note was addressed in 67930da and the thread is resolved.
Extended reasoning...
Overview
Two files touched, no runtime code. docs/runtime/utils.mdx gains a perCodePoint example, an explanatory paragraph, and the option's JSDoc entry in the inlined TypeScript definition block. test/js/bun/util/stringWidth.test.ts gains a describe("perCodePoint") block (default off, emoji-sequence per-member counts, node's soft-hyphen behavior, composition with countAnsiEscapeCodes and ambiguousIsNarrow on both Latin-1 and UTF-16 inputs) and extends the existing Object.prototype pollution test to cover the third option.
Security risks
None. Documentation prose and additive test assertions only; no native code, no user-facing behavior change, no dependency changes.
Level of scrutiny
Low. The option shipped in 1.4.0 (#34660) and is already declared in bun.d.ts; this PR only closes the documentation gap and pins the documented numbers with tests. I verified the JSDoc is copied verbatim from packages/bun-types/bun.d.ts:559-569, and traced every asserted value through StringWidth::perCodePointColumnWidth / perCodePointLatin1Width / perCodePointUTF16Width in src/jsc/bindings/stringWidth.cpp — the EAW-first ordering means skin-tone modifiers are 2 (Wide before Emoji_Modifier), soft hyphen is special-cased to 1, and Cc/Cf/Me/Mn zero out VS16/ZWJ/keycap-enclosing, matching each test expectation.
Other factors
Tests follow the file's existing conventions (exact .toBe/.toEqual, no sleeps, no network). The prototype-pollution extension is meaningful because the option is read via getIfPropertyExistsPrototypePollutionMitigation. The one prior review comment (CodeRabbit, on limiting the string-width portability claim) is addressed by the sentence added in 67930da and the thread is marked resolved. The PR description notes the tests also pass on released 1.4.0, which is expected and correct here — they pin documented behavior of an already-shipped feature rather than a runtime fix.
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Problem
Bun.stringWidthaccepts a third option,perCodePoint, since 1.4.0 (added in node compat batch: callback-throw dispatch, Assert class + native deep-equality parity, Intl gate + URL/buffer fallout, compile cache, watch kill-signal, profilers (+98 tests) #34660, declared inStringWidthOptionsinpackages/bun-types/bun.d.ts, parsed insrc/jsc/bindings/stringWidth.cpp).Bun.stringWidth()section ofdocs/runtime/utils.mdxnever mentions it. Its inlined "TypeScript definition" block lists onlycountAnsiEscapeCodesandambiguousIsNarrow, so the docs page shows an options type that is missing a shipped option (grep -rn perCodePoint docsis empty on main).test/exercised the option either.Fix
docs/runtime/utils.mdx: addperCodePointto the example block and the inlined definition (the JSDoc is copied verbatim frombun.d.ts), plus one paragraph saying what the option changes and when to use it.Bun.stringWidth("👨👩👧👦")is 2 and{ perCodePoint: true }gives 8 on both bun 1.4.0 and a debug build of main, and the example block was run line by line against its// =>annotations.console.table/util.inspectalignment" wording is the same claim the existingbun.d.tsJSDoc makes; checked by execution: everyperCodePointvalue in the new tests equals node v26.3.0'sinternalBinding("icu").getStringWidthfor the same string, and node'sconsole.tablepads a column holding that family emoji to 8 columns.test/js/bun/util/stringWidth.test.ts: newperCodePointblock pinning the documented values: off by default, each member of an emoji sequence counted, node's per-code-point widths (including soft hyphen as one column), and composition withcountAnsiEscapeCodesandambiguousIsNarrowon both the Latin-1 and UTF-16 string paths. The existingObject.prototypepollution test now covers the third option too.ambiguousIsNarrowJSDoc line in the same block is stale relative tobun.d.ts; docs: correct typo #30696 already rewrites it, so this PR leaves that line alone (the two apply cleanly together). bun-types: fix the family emoji width in the stringWidth example #38388 fixes thebun.d.ts@exampleand does not touch the docs.bun bd test test/js/bun/util/stringWidth.test.ts(179 pass). The runtime is unchanged, so the new tests also pass on the released 1.4.0; they pin documented behavior rather than prove a runtime fix.Background
Bun.stringWidthreturns the number of terminal columns a string occupies. By default it measures per grapheme cluster (what a terminal renders as one glyph), matching thestring-widthnpm package: an emoji ZWJ sequence such as the family emoji is one cluster, 2 columns wide.perCodePoint: trueswitches to node'sGetColumnWidthalgorithm (src/node_i18n.cc): each code point is measured on its own using its East Asian Width property plus Emoji_Presentation, with controls, format characters and combining marks counting as zero. The family emoji is four 2-column emoji joined by three zero-width ZWJs, so it measures 8. Node uses this forconsole.tableandutil.inspect, which is why the option exists.bun.d.ts, so it has to be updated by hand whenever an option is added.