hermes-eslint

library0.35.0jsnpmunverified

A custom ESLint parser using the Hermes JavaScript parser, optimized for linting Flow-typed code. Version 0.35.0 is current, with active development on GitHub (facebook/hermes). Unlike babel-eslint or @babel/eslint-parser, hermes-eslint uses Hermes' own parser, ensuring precise adherence to Flow syntax and avoiding potential mismatches. It supports JSX, Flow, and modern ECMAScript features, with options for jsxPragma, jsxFragmentName, sourceType, and FBT. It is the recommended parser for Facebook's internal linting and for projects heavily reliant on Flow.

testing

npm install hermes-eslint

package ↗

INSTALL

IMPORT

SIG · HERMES-ESLINT

hermes-eslint

testingjavascriptv0.35.0

Install

—

Import

—

Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

default export (parser)

✓ { "parser": "hermes-eslint" }

✗ { "parser": require('hermes-eslint') }

In .eslintrc, specify the parser as a string, not a require call. hermes-eslint is used as an ESLint parser, not imported in code.

ParserOptions type

✓ import type { ParserOptions } from 'hermes-eslint'

✗ import { ParserOptions } from 'hermes-eslint'

ParserOptions is a type-only export; use import type or import {} from if not using runtime. Alternatively, use eslint's built-in types.

parseForESLint function

✓ import { parseForESLint } from 'hermes-eslint'

✗ const parseForESLint = require('hermes-eslint').parseForESLint;

ESM-only; requires module resolution. parseForESLint is used internally by ESLint, but can be called directly for custom integrations.

Configures ESLint to use hermes-eslint as parser with module source type and React JSX pragma.

// .eslintrc.json { "parser": "hermes-eslint", "parserOptions": { "sourceType": "module", "jsxPragma": "React" }, "rules": { "no-unused-vars": "error", "flowtype/no-types-missing-file-annotation": "off" } }

Debug

Known issues

breakingVersion 0.10.0 dropped support for ESLint < 6.

fix

Upgrade ESLint to 6.x or later and use hermes-eslint >=0.10.0.

affects: <0.10.0

deprecatedThe option 'useJSXTextNode' was removed in version 0.15.0.

fix

Remove 'useJSXTextNode' from parserOptions; it is no longer necessary.

affects: >=0.15.0

gotchaIf using Flow with hermes-eslint, ensure your ESLint config does not conflict with babel-eslint; both parsers may be active.

fix

Set 'parser' to 'hermes-eslint' only for .js/.jsx files; use override patterns if mixing with Babel.

affects: all

gotchaESLint's --fix may produce unexpected results with Flow type syntax; some rules may not support autofix.

fix

Test --fix on a small file first; disable autofix for rules known to conflict with Flow.

affects: all

deprecatedThe 'experimentalObjectRestSpread' option is no longer needed as of ECMAScript 2018.

fix

Remove the option; modern parsers support object rest/spread natively.

affects: all

Errors

Common errors & fixes

Error: Cannot find module 'hermes-eslint'

hermes-eslint not installed or ESLint cannot resolve the parser.

fix

Run 'npm install --save-dev hermes-eslint' or ensure it's in your package.json.

Error: Failed to load parser 'hermes-eslint' (from .eslintrc)

Incorrect JSON syntax in .eslintrc or parser name is not a string.

fix

Verify .eslintrc JSON is valid and that 'parser' is set to exactly "hermes-eslint".

TypeError: parseForESLint is not a function

Importing the module incorrectly in a CommonJS environment.

fix

Use dynamic import: const { parseForESLint } = await import('hermes-eslint'); or ensure you are in an ESM context.

Upgrade

Version history

0.35.0latest on npm

Audit

Dependencies

eslintrequiredPeer dependency; hermes-eslint is a custom parser that integrates with ESLint's parsing interface.

Agent activity

8 hits · last 30 days

node

Resources

packagehttps://www.npmjs.com/package/hermes-eslint ↗