ESLint 9.0: A major update with new features, breaking changes, and deprecated elements

ESLint, the widely-used tool for static analysis of JavaScript code, has recently unveiled its version 9.0. This significant release brings new features, resolves various bugs from the prior version, and introduces multiple breaking changes.

ESLint 9.0 discontinues support for all Node.js versions earlier than v18.18.0 and v19.x, coinciding with the LTS release of Node.js v20.x.

The update also transitions to Flat config as the default configuration format, officially deprecating eslintrc. This alteration impacts users, plugin developers, and integrators, necessitating numerous changes in ESLint. The release further includes a config inspector, accessible via the command line using the --inspect-config option.

Several formatters have been removed in ESLint 9.0, including checkstyle, compact, jslint-xml, junit, tap, unix, and visualstudio. Users currently employing these formatters will need to install standalone packages compatible with ESLint version 9.0.

The version also discontinues valid-jsdoc and require-jsdoc, proposing the use of the eslint-plugin-jsdoc as an alternative.

Moreover, ESLint 9.0 has replaced many of the deprecated methods from context with methods on SourceCode.

Additionally, the release includes a range of minor changes, enhancements, and bug fixes.