v8.0.0

Major Changes

• abb8263: ESM-only package, with flat config (eslint.config.js) support.

  What changed

  • The package is now ESM only. It exports configs, rules and meta as
    named exports and the plugin object as the default export, which is what
    eslint.config.js, @eslint/eslintrc and eslint --plugin harmony each need.
    There is no require entry point.
  • Node.js ^20.19.0 || ^22.13.0 || >=24 is required. Older versions cannot
    require() an ESM package, which is how ESLint 8 and 9 load a plugin from an
    .eslintrc.
  • The eslint peer range is now >=8.57.0. The old >=8.4.0 could not be true
    once loading the plugin depends on require(esm).
  • New flat/* configs: flat/recommended, flat/latest, flat/es5,
    flat/es5-strict, flat/ts-recommended, flat/ts-recommended-type-check,
    flat/ts-recommended-requiring-type-checking, flat/ts-recommended-cra,
    flat/ts-recommended-type-check-cra and flat/ts-prettier.
  • harmony/ts-member-delimiter-style now reads context.sourceCode, so it runs
    on ESLint 10, which removed context.getSourceCode().
  • The eslintrc configs (plugin:harmony/*) are unchanged.

  Migrating

  If you use eslint.config.js

  import { defineConfig } from 'eslint/config'
  import harmony from 'eslint-plugin-harmony'
  
  export default defineConfig([
    {
      files: ['**/*.js'],
      plugins: { harmony },
      extends: ['harmony/recommended'],
    },
  ])

  extends: ['harmony/<name>'] resolves the flat/<name> config on ESLint 9.23
  and later. On earlier versions, spread it instead:
  export default [...harmony.configs['flat/recommended']].

  The flat configs are overlays: they carry only the rules harmony sets. The bases
  the eslintrc configs extended by name — eslint:recommended,
  plugin:@typescript-eslint/*, prettier — have no string form in flat config,
  so compose them yourself, with harmony last. The ts-* flat configs in
  particular set @typescript-eslint/* rules but register neither the plugin nor
  a parser: put typescript-eslint's own configs before them.

  Two further differences from the eslintrc twins: the ts-* flat configs scope
  themselves to **/*.{ts,tsx,mts,cts}, and no ecmaVersion is pinned except in
  es5 and es5-strict — the eslintrc ES2018/ES2019 floors would have won over
  yours in flat config and broken modern syntax.

  If you use .eslintrc

  Nothing about plugin:harmony/* changed, but ESLint 10 removed the eslintrc
  format entirely (ESLINT_USE_FLAT_CONFIG=false no longer brings it back), so
  staying on .eslintrc means staying on ESLint 8 or 9. Node.js must be at least
  20.19 for ESLint to load this package from an .eslintrc at all.

  If you use a CommonJS config file

  require('eslint-plugin-harmony') still works on the Node versions this package
  supports — require() of an ESM package returns the module namespace there — but
  the plugin object is now require('eslint-plugin-harmony').default. On older
  Node it throws ERR_REQUIRE_ESM. Prefer an eslint.config.mjs with
  import harmony from 'eslint-plugin-harmony'.

  Dependencies

  • @typescript-eslint/experimental-utils (deprecated, v5) is replaced by
    @typescript-eslint/utils v8. It is what the custom rule is built on, and its
    eslint peer range (^8.57.0 || ^9 || ^10) matches this package's own — v5's
    did not. If you import this package's types, the rules record is now typed
    with TSESLint.RuleModule from @typescript-eslint/utils.
  • @rushstack/eslint-patch is dropped. Nothing in this package used it.
  • @typescript-eslint/eslint-plugin is now an optional peer dependency. Only
    the ts-* configs need it; harmony/recommended on plain JavaScript does not.
    The range is unchanged (>= 6.0.0), and the ts-* configs are verified
    against v6 through v8.

  typescript-eslint v8

  @typescript-eslint/parser (a real dependency of this package) and the
  @typescript-eslint/eslint-plugin this repo tests against both move to ^8.
  The @typescript-eslint/eslint-plugin peer range is unchanged (>= 6.0.0), so
  nothing forces you off v6 or v7.

  Why the parser bump matters

  @typescript-eslint/parser@^6 cannot run on ESLint 10 — it throws
  scopeManager.addGlobals is not a function. eslintrc consumers resolve the
  parser named in style-parts/ts-common.json from this package, so the pinned
  v6 was theirs whether they wanted it or not. v8's parser is verified working on
  ESLint 8.57.1, 9.39.5 and 10.10.0.

  Rule changes

  Only one rule entry was added, and it is additive — an off for a rule id that
  does not exist in v6 or v7 is a no-op there, so resolved severities on those
  versions are unchanged:

  • @typescript-eslint/no-empty-object-type: "off" in ts-common, beside the
    existing @typescript-eslint/no-empty-interface: "off". v8 dropped
    no-empty-interface from plugin:@typescript-eslint/recommended and replaced
    it with no-empty-object-type (which also absorbed part of the removed
    ban-types). Without the new entry, this package's long-standing decision that
    empty interfaces are allowed — they carry contextual meaning and leave room to
    extend without a breaking change — was silently lost on v8. Note the
    replacement is broader than what it replaces: {} as a type annotation is now
    allowed too, because the rule is off rather than narrowed.

  Two entries in ts-common are now inert rather than wrong, and are kept for v6
  and v7 consumers:

  • @typescript-eslint/indent: "off" and
    @typescript-eslint/member-delimiter-style: "off". Both rules were moved out
    of typescript-eslint into @stylistic and no longer exist in v8. ESLint
    ignores an unknown rule set to severity 0, so they stay harmless. They are
    not re-expressed as @stylistic/* entries: this package does not depend on
    @stylistic/eslint-plugin, and in flat config a rule from an unregistered
    plugin is a hard config error even at severity off.

  Everything else ts-common and the ts-recommended* configs name still exists
  in v8: ban-ts-comment, explicit-function-return-type,
  explicit-module-boundary-types, no-empty-function, no-explicit-any,
  no-namespace, no-non-null-assertion, no-unused-vars, no-use-before-define,
  no-unsafe-argument, no-unsafe-member-access.

  What v8 turns on that this package does not turn off

  The ts-* configs extend plugin:@typescript-eslint/recommended and
  plugin:@typescript-eslint/recommended-requiring-type-checking by name, so they
  follow whichever typescript-eslint version you install. Moving to v8 therefore
  brings its enlarged recommended set with it: no-unused-expressions,
  no-require-imports, no-unsafe-function-type, no-wrapper-object-types,
  no-duplicate-enum-values, no-unsafe-declaration-merging and
  no-unnecessary-type-constraint, plus the type-checked additions
  (only-throw-error, prefer-promise-reject-errors, no-unsafe-unary-minus,
  no-array-delete, and others). This package makes no judgement on those; turn
  off what you do not want.

  plugin:@typescript-eslint/recommended-requiring-type-checking, which
  ts-recommended-type-check and its siblings extend, is a deprecated alias for
  recommended-type-checked in v8. It still resolves, but expect it to go in
  typescript-eslint v9.

  Flat ts-* configs still set no parser

  Unchanged, and deliberately so: the flat ts-* configs register neither
  @typescript-eslint nor a parser, so you compose typescript-eslint's own
  configs before them. Registering a parser or plugin instance here would fight the
  one you install — Cannot redefine plugin — and would pin the parser this
  package happens to depend on over yours.