ESLint Config JValue

The eslint config reused across JValue projects.

Our general goals of linting are:

• Avoiding common code errors
• Improving the overall type safety
• Having uniform code formatting
• Avoiding unnecessary code complexity

Furthermore, we strive to avoid rules that are overly restrictive and do not contribute to the goals above.

How to use

You essentially need to perform the following steps (they will be explained in more detail in the following sections):

1. Install this package
2. Install required additional packages
3. Create a .prettierrc.js file
4. Create a .eslintrc.js file
5. Extend your tsconfig.json file

Install this package

To install this package, simply run npm install --save-dev @jvalue/eslint-config-jvalue.

Install required additional packages

This package provides three configs: One for plain TypeScript projects, one for Vue+TypeScript and one for React+TypeScript. Depending on which project you are working on, you need to install the following additional npm packages as devDependencies (i.e. using the --save-dev flag):

Project type	Required packages
TypeScript only	@typescript-eslint/eslint-plugin @typescript-eslint/parser eslint eslint-config-prettier eslint-plugin-import eslint-plugin-prettier prettier For copy-and-paste: npm install --save-dev @typescript-eslint/eslint-plugin @typescript-eslint/parser eslint eslint-config-prettier eslint-plugin-import eslint-plugin-prettier prettier
Vue+TypeScript	You need the same packages as in the "TypeScript only" config, plus: @vue/cli-plugin-eslint @vue/eslint-config-typescript eslint-plugin-vue For copy-and-paste: npm install --save-dev @typescript-eslint/eslint-plugin @typescript-eslint/parser eslint eslint-config-prettier eslint-plugin-import eslint-plugin-prettier prettier @vue/cli-plugin-eslint @vue/eslint-config-typescript eslint-plugin-vue
React+TypeScript	Are you using Create-React-App? Then you only need the following packages: eslint-config-prettier eslint-plugin-prettier prettier For copy-and-paste: npm install --save-dev eslint-config-prettier eslint-plugin-prettier prettier If you are not using Create-React-App, then you additionally need to install eslint-config-react-app.

The list of packages you need may change in the future. We recommend you take a look at this list (and the release notes) whenever you upgrade to a newer version of @jvalue/eslint-config-jvalue.

Create a .prettierrc.js file

After you have installed all packages, create a .prettierrc.js file with the following content:

module.exports = require('@jvalue/eslint-config-jvalue/.prettierrc.js');

Create a .eslintrc.js file

Finally, you need to create a .eslintrc.js file. Again, we distinguish plain TypeScript projects, projects using Vue+TypeScript, and projects using React+TypeScript.

File content for plain TypeScript projects

module.exports = {
  extends: '@jvalue/eslint-config-jvalue',
};

File content for Vue+TypeScript projects

module.exports = {
  extends: '@jvalue/eslint-config-jvalue/vue',
};

File content for React+TypeScript projects

module.exports = {
  extends: '@jvalue/eslint-config-jvalue/react',
};

Extend your tsconfig.json file

Finally, it is highly recommended that you add the following settings to the compilerOptions section of your tsconfig.json file:

"strict": true,
"noImplicitOverride": true,
"noUncheckedIndexedAccess": true,
"exactOptionalPropertyTypes": true,
"noFallthroughCasesInSwitch": true,

Now, you can finally start linting your project.

Tips and tricks

Overriding rules

In some cases, certain linter rules are not suitable for your project. Or, you want to use an additional rule. You can easily override certain rules in your .eslintrc.js using the overrides section in .eslintrc.js. An example:

module.exports = {
  extends: '@jvalue/eslint-config-jvalue',
  overrides: [
    {
      files: ['*.ts'],
      rules: {
        'capitalized-comments': 'off',
      },
    },
  ],
};

Here, rule capitalized-comments is turned off for all .ts files.

npm script

In a TypeScript or React+TypeScript project, add the following to the scripts section of your package.json:

"lint": "eslint src --max-warnings=0"

Now, when running npm run lint, your project files will get linted. (We assume that your project files are all stored in folder src/).

In a Vue+TypeScript project, use the following instead:

"lint": "vue-cli-service lint --no-fix --max-warnings=0"

VSCode extensions

If you are using VSCode, we recommend installing the following extensions:

• vscode-eslint
• prettier

VSCode auto formatting

When developing, you often don't want to spend time manually formatting your code. If you are using VSCode, you can automate this process. Create a new file .vscode/settings.json and paste the following:

{
  "eslint.validate": ["typescript"],
  "typescript.preferences.importModuleSpecifier": "relative",
  "[css]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[javascript]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[json]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[jsonc]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[markdown]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[scss]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "esbenp.prettier-vscode"
  },
  "[typescript]": {
    "editor.formatOnSave": false,
    "editor.defaultFormatter": "esbenp.prettier-vscode",
    "editor.codeActionsOnSave": ["source.fixAll.format", "source.fixAll.eslint"]
  },
  "[typescriptreact]": {
    "editor.formatOnSave": false,
    "editor.defaultFormatter": "esbenp.prettier-vscode",
    "editor.codeActionsOnSave": ["source.fixAll.format", "source.fixAll.eslint"]
  },
  "[vue]": {
    "editor.formatOnSave": false,
    "editor.defaultFormatter": "esbenp.prettier-vscode",
    "editor.codeActionsOnSave": ["source.fixAll.format", "source.fixAll.eslint"]
  }
}

Now, whenever you save a file, all automatically fixable linter errors will be fixed.

Development

This section contains information regarding the development of this package. If you are only intending to use this package, but not to make changes to it, then you can skip this section.

File structure

There are three files where our configs are stored: index.js, react.js, and vue.js. When a developer uses this package and writes extends: '@jvalue/eslint-config-jvalue', then the index file is loaded. When using extends: '@jvalue/eslint-config-jvalue/react' or extends: '@jvalue/eslint-config-jvalue/vue', the config found in react.js or vue.js is loaded.

You will notice that the rules found in these three files are in many places just copies (i.e. the list of rules in index.js is very similar to react.js and vue.js). This is mostly done to simplify the structure of this project. If you add a new rule, you probably need to add it to all three configs.

Testing

Before publishing a new config, it is highly recommended that you test it in a project to determine if the config really matches your expectations. A suggestion: Create a new TypeScript/React/Vue project in a directory outside of eslint-config-jvalue. Here, you can import your local eslint config and test if it works properly.

To import the eslint config, you could simply symlink eslint-config-jvalue in your package.json using something like "@jvalue/eslint-config-jvalue": "file:../(path-to-the-eslint-config-folder)" as a devDependency. However, this might lead to issues in some setups. Instead, and in order to better predict the actual package structure, it is recommended to do the following:

1. In the eslint-config-jvalue folder, run npm pack. This will create a .tgz file.
2. In your test project, run npm install --save-dev ../(path-to-the-eslint-config-folder)/the-tgz-file.tgz (substituting (path-to-the-eslint-config-folder) with the actual path, and the-tgz-file.tgz with the name of the file created in the previous step)
3. Now, you can use this package like an external package and test whether it fulfills your expectations.