eslint breaking changes

npm

3 curated breaking changes across major versions of eslint. Use this as a migration checklist before bumping dependencies.

changes

Breaking changes by transition

8 \u2192 9config
Flat config (eslint.config.js) is the default; legacy .eslintrc.* no longer read unless ESLINT_USE_FLAT_CONFIG=false.
Migration
Migrate with `npx @eslint/migrate-config .eslintrc.json`. Or export `ESLINT_USE_FLAT_CONFIG=false` temporarily.
8 \u2192 9removal
Many formatting rules removed (moved to @stylistic/eslint-plugin). Use Prettier or @stylistic for formatting.
Migration
`npm i -D @stylistic/eslint-plugin` and import its rules, or defer formatting to Prettier.
8 \u2192 9runtime
Node.js 18.18+ required.
Migration
Upgrade Node first. formatter and custom rule APIs also changed — check plugins for eslint@9 support.

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