How to configure package.json to run eslint script
eslint "**/*.js" to run on all js files in all the folders recursively (in the current folder)
You can also do: AnyFolder/**/*.js
And to ignore a folder: eslint "**/*.js" --ignore-pattern node_modules/
Know more at eslint/command-line-interface
eslint . --ext .js to lint files with the .js extension.
The . targets files in the current directory and all subdirectories.
To include other file extensions,eslint . --ext .js,.jsx or eslint . --ext .js --ext .jsx.
The eslint documentation covers this option.
I'm not sure if the accepted answer is outdated, but by looking at the docs,
By default, it uses .js as the only file extension.
Also, according to a member's comment on the project's Github, using . equals running in all subdirectories. It seems to me that running eslint . should suffice (though it doesn't cover the new ES Module .mjs files).