@preco21/eslint-config - moved to @preco21/eslint-config

ESLint shareable config for @preco21

This package provides @preco21's ESLint rules as an extensible shared config.

Install

npm install --save-dev @preco21/eslint-config

Peer dependencies

If you are only interested in the default config (base), you are good to go and you don’t need to follow installation instructions below.

There are configs that work with various plugins like typescript, import, react, and so on.

To use those, you will need to install all its peer dependencies.

By default, to prevent installing unnecessary peer dependencies, all listed peer dependencies (except the eslint itself) are marked as optional via peerDependenciesMeta field in the package.json. And it's recommended to install only peer dependencies that you are going to use.

Install the correct versions of each package, which are listed by the command:

npm info "@preco21/eslint-config@latest" peerDependencies

If using npm 5+, use this shortcut:

npx install-peerdeps --dev @preco21/eslint-config

For more details about the installation, please refer to Airbnb's ESLint config documentation.

Usage

Add some ESLint config to your package.json:

{
  "eslintConfig": {
    "root": true,
    "extends": "@preco21/eslint-config"
  }
}

Or to .eslintrc:

{
  "root": true,
  "extends": "@preco21/eslint-config"
}

You can find more details about ESLint configuration here.

Available configs

The package exposes a number of configs along with the base one.

There are two types of the config:

• concrete: A config that just works without any extra configuration.
• composable: A config that can be composed to make customized configuration.

Concrete configs

[WIP]

You can find concrete configs in the top-level of the package:

{
  "extends": "@preco21/eslint-config"
}

• @preco21/eslint-config: The basic config for common JavaScript projects. This config is assuming you are in node environment (e.g. nodejs, webpack, ...).
• @preco21/eslint-config/react: The config for React projects with support for React and JSX.
• @preco21/eslint-config/react-native: The config for ReactNative projects with support for React and JSX.

Every concrete config has ECMAScript modules support and latest ECMAScript features enabled by default.

Composable configs

If the concrete rules don't support your use-cases, you may use composable configs from the rules folder to assemble your own config:

{
  "extends": [
    "@preco21/eslint-config/rules/base",
    "@preco21/eslint-config/rules/typescript",
    ...
  ]
}

It's recommended to use other configs upon the base config, since it contains sensible default rules to work with.

Please note that you may need to configure extra options like env or parserOptions as needed.

For example:

{
  "env": {
    "es6": true,
    "node": true
  },
  "parserOptions": {
    "ecmaVersion": 2019,
    "sourceType": "module"
  },
  "extends": [
    "@preco21/eslint-config/rules/base",
    "@preco21/eslint-config/rules/typescript"
  ]
}

Also, you may need to install optional plugins to use some config. (see install section)

Tips

Browser

If you are in browser environment, you can add browser option to env field:

{
  "env": {
    "browser": true
  }
}

• Why there's no such thing like @preco21/eslint-config/browser?

Using globals

As ESLint makes no assumptions about what global variables exist in your execution environment, you will need to provide knowledge of what global variables are available. (e.g. referring external library at runtime)

You can define global variables in your configuration as follows:

{
  "globals": {
    "$": "readonly"
  }
}

For each global variable key, set the corresponding value equal to writable to allow the variable to be overwritten or readonly to disallow overwriting.

See here for more details.

Using script source type

Every concrete configs treats your code as ECMAScript modules enabled environment by default. Add this to your configuration if you want to disable it:

{
  "parserOptions": {
    "sourceType": "script"
  }
}

Using ECMAScript 5

Although this is not generally recommended, you can fallback to ECMAScript 5 by adding this to your configuration:

{
  "extends": [
    "@preco21/eslint-config/rules/base",
    "@preco21/eslint-config/rules/with-es5"
  ]
}

Please note that the with-es5 config automatically enables strict rule.

Note: However, ESLint might still show unexpected errors or warnings because the rules in this config were defined under the assumption that users will be writing ES2015+ code. In this case, you can safely disable the problematic rules manually.

Enforcing strict mode

We don't enable the strict rule by default for reason: Today, we all use tooling like webpack, Babel, and languages like TypeScript. And these tools automatically insert a 'use strict' directive for each source to ensure your code is in strict mode.

Also, ECMAScript modules enabled environments are strict mode by default.

So, enabling strict rule to ensure if the 'use strict' directive is properly placed in your source doesn't really help but redundant.

But, often you do need the rule for writing non-compiled code like CLI scripts.

Then, you can optionally enable the rule for the specific case:

{
  "overrides": [
    {
      "files": ["bin/**/*.js"],
      "parserOptions": {
        "sourceType": "script",
        "ecmaFeatures": {
          "jsx": false
        }
      },
      "rules": {
        "strict": "error"
      }
    }
  ]
}

Electron

If you are in Electron environment, you may need to add electron to import/core-modules setting. So that eslint-import-plugin can consider the electron module as a core module like path:

{
  "settings": {
    "import/core-modules": ["electron"]
  }
}

For more details, see here.