fix: handle new of conflict cases by guybedford · Pull Request #195 · guybedford/es-module-lexer

guybedford · 2025-12-07T08:50:57Z

Resolves #188 — of as an identifier on the LHS of / inside a for header was being mis-parsed as the for-of contextual keyword, causing the / to be treated as the start of a regex.

Approach

Inside for (...), of is the for-of contextual keyword only if it follows a binding. In valid JS a binding always ends with one of:

An identifier-tail char (alphanumeric, _, $)
] (array destructuring)
} (object destructuring)
) (parenthesized binding)

Anything else means of is just an identifier and the following / is division. New isForOfBinding helper scans backward through whitespace from the char before of and checks that terminator.

Cases now covered

C-style for, of as identifier (the / is division):

for (i = of / 2;;) break       // = before of
for (; of / 2;) break           // ; before of
for (;; of / 2) break           // ; before of
for (i + of / 2;;) break        // any binary operator
for (i, of / 2;;) break         // comma
for (i < of / 2;;) break
for (i | of / 2;;) break
for (i ? of / 2 : 0;;) break
for ((of) / 2;;) break          // parenthesized identifier

For-of with regex iterable (the /regex/ is still recognized as a regex):

for (i of /regex/) break
for (let x of /regex/) break
for ([a] of /regex/) break
for ({a} of /regex/) break
for ((x) of /regex/) break
for(let t of/[0-9]+/g.exec(e)){}     // existing test, no space before /
for ([x]of /regex/) break             // no space between ] and of
for (i  of /regex/) break             // multiple spaces
for (i\tof /regex/) break             // tab
for (i\nof /regex/) break             // newline

Disambiguate `of` as identifier vs for-of contextual keyword inside `for (...)` by checking whether `of` actually follows a binding (the only place the for-of keyword can appear). In valid JS a binding always ends with an identifier-tail char, ']', '}', or ')' — anything else means `of` is just an identifier and the following `/` is division, not the start of a regex. Adds isForOfBinding which scans backward through whitespace from the char before `of` and checks that terminator. This is more robust than the previous fixed-offset exclusion list (which only excluded ';' and '=', missing '+', '-', '*', ',', '<', '|', '&', '?', etc.) and also handles tab/newline whitespace and the no-space-before-of cases like `for ([x]of /regex/)`. Fixes #188.

…2.1.0 in /studio [skip ci] Bumps [es-module-lexer](https://github.com/guybedford/es-module-lexer) from 2.0.0 to 2.1.0. Release notes *Sourced from [es-module-lexer's releases](https://github.com/guybedford/es-module-lexer/releases).* > 2.1.0 > ----- > > What's Changed > -------------- > > * Always exclude dyn import attributes from specifier range by [`@nicolo-ribaudo`](https://github.com/nicolo-ribaudo) in [guybedford/es-module-lexer#197](https://redirect.github.com/guybedford/es-module-lexer/pull/197) > * fix: handle new of conflict cases by [`@guybedford`](https://github.com/guybedford) in [guybedford/es-module-lexer#195](https://redirect.github.com/guybedford/es-module-lexer/pull/195) > > New Contributors > ---------------- > > * [`@nicolo-ribaudo`](https://github.com/nicolo-ribaudo) made their first contribution in [guybedford/es-module-lexer#197](https://redirect.github.com/guybedford/es-module-lexer/pull/197) > > **Full Changelog**: <guybedford/es-module-lexer@2.0.0...2.1.0> Commits * [`5fb11e1`](guybedford/es-module-lexer@5fb11e1) 2.1.0 * [`cc29c5b`](guybedford/es-module-lexer@cc29c5b) fix: handle new of conflict cases ([#195](https://redirect.github.com/guybedford/es-module-lexer/issues/195)) * [`4a35138`](guybedford/es-module-lexer@4a35138) Always exclude dyn import attributes from specifier range ([#197](https://redirect.github.com/guybedford/es-module-lexer/issues/197)) * See full diff in [compare view](guybedford/es-module-lexer@2.0.0...2.1.0) [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility\_score?dependency-name=es-module-lexer&package-manager=npm\_and\_yarn&previous-version=2.0.0&new-version=2.1.0)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- Dependabot commands and options You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot show ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

…2.1.0 in /studio [skip ci] Bumps [es-module-lexer](https://github.com/guybedford/es-module-lexer) from 2.0.0 to 2.1.0. Release notes *Sourced from [es-module-lexer's releases](https://github.com/guybedford/es-module-lexer/releases).* > 2.1.0 > ----- > > What's Changed > -------------- > > * Always exclude dyn import attributes from specifier range by [`@nicolo-ribaudo`](https://github.com/nicolo-ribaudo) in [guybedford/es-module-lexer#197](https://redirect.github.com/guybedford/es-module-lexer/pull/197) > * fix: handle new of conflict cases by [`@guybedford`](https://github.com/guybedford) in [guybedford/es-module-lexer#195](https://redirect.github.com/guybedford/es-module-lexer/pull/195) > > New Contributors > ---------------- > > * [`@nicolo-ribaudo`](https://github.com/nicolo-ribaudo) made their first contribution in [guybedford/es-module-lexer#197](https://redirect.github.com/guybedford/es-module-lexer/pull/197) > > **Full Changelog**: <guybedford/es-module-lexer@2.0.0...2.1.0> Commits * [`5fb11e1`](guybedford/es-module-lexer@5fb11e1) 2.1.0 * [`cc29c5b`](guybedford/es-module-lexer@cc29c5b) fix: handle new of conflict cases ([ArcadeData#195](https://redirect.github.com/guybedford/es-module-lexer/issues/195)) * [`4a35138`](guybedford/es-module-lexer@4a35138) Always exclude dyn import attributes from specifier range ([ArcadeData#197](https://redirect.github.com/guybedford/es-module-lexer/issues/197)) * See full diff in [compare view](guybedford/es-module-lexer@2.0.0...2.1.0) [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility\_score?dependency-name=es-module-lexer&package-manager=npm\_and\_yarn&previous-version=2.0.0&new-version=2.1.0)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- Dependabot commands and options You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot show ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

guybedford mentioned this pull request Dec 7, 2025

Parse error in for statement when identifier of is divided #188

Closed

guybedford force-pushed the parse-case branch from 174609c to adc94af Compare April 25, 2026 21:13

guybedford force-pushed the parse-case branch from adc94af to c541b4a Compare April 25, 2026 21:20

guybedford merged commit cc29c5b into main Apr 25, 2026
1 check passed

guybedford deleted the parse-case branch April 25, 2026 21:23

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fix: handle new of conflict cases#195

fix: handle new of conflict cases#195
guybedford merged 1 commit into
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parse-case

guybedford commented Dec 7, 2025 •

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guybedford commented Dec 7, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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guybedford commented Dec 7, 2025 •

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