Migrating Eslint to v9

Use the auto-migration tool:

npx @eslint/migrate-config .eslintrc

It will migrate your .eslintrc config file to the new eslint v9 flatConfig format.

Make sure it works as expected, you may have to remove some ignore comments and so on.

Also remove the old config and check that the new config is picked up by your IDE and cli tool.

Using eslint v9 with vite-plugin-checker

You will need to add the useFlatConfig: true to the plugin config:

import { UserConfigExport, defineConfig } from 'vite';
import checker from 'vite-plugin-checker';

// https://vitejs.dev/config/
export default (): UserConfigExport => {
  return defineConfig({
    plugins: [
      checker({
        eslint: {
          // 👇 Need to add this line
          useFlatConfig: true, 
          // rest of your config ...
        },
        // config of other tools supported by checker
      })
      // other plugins ...
    ],
  });
};