.eslintrc.js

//
// SlackAPI JavaScript style
// ---
// This style helps maintainers enforce safe and consistent programming practices in this project. It is not meant to be
// comprehensive on its own or vastly different from existing styles. The goal is to inherit and aggregate as many of
// the communities' recommended styles for the technologies used as we can. When, and only when, we have a stated need
// to differentiate, we add more rules (or modify options). Therefore, the fewer rules directly defined in this file,
// the better.

module.exports = {
  // This is a root of the project, ESLint should not look through parent directories to find more config
  root: true,

  ignorePatterns: [
    // Ignore all build outputs and artifacts (node_modules, dotfiles, and dot directories are implicitly ignored)
    '/dist',
    '/coverage',
  ],

  // These environments contain lists of global variables which are allowed to be accessed
  env: {
    // According to https://node.green, the target node version (v10) supports all important ES2018 features. But es2018
    // is not an option since it presumably doesn't introduce any new globals over ES2017.
    es2017: true,
    node: true,
  },

  extends: [
    // ESLint's recommended built-in rules: https://eslint.org/docs/rules/
    'eslint:recommended',

    // Node plugin's recommended rules: https://github.com/mysticatea/eslint-plugin-node
    'plugin:node/recommended',

    // AirBnB style guide (without React) rules: https://github.com/airbnb/javascript.
    'airbnb-base',

    // JSDoc plugin's recommended rules
    'plugin:jsdoc/recommended',
  ],

  rules: {
    // JavaScript rules
    // ---
    // The top level of this configuration contains rules which apply to JavaScript (and will also be inherited for
    // TypeScript). This section does not contain rules meant to override options or disable rules in the base
    // configurations (ESLint, Node, AirBnb). Those rules are added in the final override.

    // Eliminate tabs to standardize on spaces for indentation. If you want to use tabs for something other than
    // indentation, you may need to turn this rule off using an inline config comments.
    'no-tabs': 'error',

    // Bans use of comma as an operator because it can obscure side effects and is often an accident.
    'no-sequences': 'error',

    // This repo uses console.log, which is fine to do in GitHub actions
    'no-console': 'off',

    // Disallow the use of process.exit()
    'node/no-process-exit': 'error',

    // Allow safe references to functions before the declaration. Overrides AirBnB config. Not located in the override
    // section below because a distinct override is necessary in TypeScript files.
    'no-use-before-define': ['error', 'nofunc'],
  },

  overrides: [
    {
      files: ['**/*.js'],
      rules: {
        // Override rules
        // ---
        // This level of this configuration contains rules which override options or disable rules in the base
        // configurations in JavaScript.

        // Increase the max line length to 120. The rest of this setting is copied from the AirBnB config.
        'max-len': ['error', 120, 2, {
          ignoreUrls: true,
          ignoreComments: false,
          ignoreRegExpLiterals: true,
          ignoreStrings: true,
          ignoreTemplateLiterals: true,
        }],

        // Restrict the use of backticks to declare a normal string. Template literals should only be used when the
        // template string contains placeholders. The rest of this setting is copied from the AirBnb config.
        quotes: ['error', 'single', { avoidEscape: true, allowTemplateLiterals: false }],

        // the server side Slack API uses snake_case for parameters often
        // for mocking and override support, we need to allow snake_case
        // Allow leading underscores for parameter names, which is used to acknowledge unused variables in TypeScript.
        // Also, enforce camelCase naming for variables. Ideally, the leading underscore could be restricted to only
        // unused parameter names, but this rule isn't capable of knowing when a variable is unused. The camelcase and
        // no-underscore-dangle rules are replaced with the naming-convention rule because this single rule can serve
        // both purposes, and it works fine on non-TypeScript code.
        camelcase: 'off',
        'no-underscore-dangle': 'off',

        // Remove the minProperties option for enforcing line breaks between braces. The AirBnB config sets this to 4,
        // which is arbitrary and not backed by anything specific in the style guide. If we just remove it, we can
        // rely on the max-len rule to determine if the line is too long and then enforce line breaks. Overrides AirBnB
        // styles.
        'object-curly-newline': ['error', { multiline: true, consistent: true }],
      },
    },
    {
      files: ['src/test/*.js'],
      rules: {
        // Test-specific rules
        // ---
        // Rules that only apply to JavaScript _test_ source files

        // With Mocha as a test framework, it is sometimes helpful to assign
        // shared state to Mocha's Context object, for example in setup and
        // teardown test methods. Assigning stub/mock objects to the Context
        // object via `this` is a common pattern in Mocha. As such, using
        // `function` over the the arrow notation binds `this` appropriately and
        // should be used in tests. So: we turn off the prefer-arrow-callback
        // rule.
        // See https://github.com/slackapi/bolt-js/pull/1012#pullrequestreview-711232738
        // for a case of arrow-vs-function syntax coming up for the team
        'prefer-arrow-callback': 'off',

        // Using ununamed functions (e.g., null logger) in tests is fine
        'func-names': 'off',
        // In tests, don't force constructing a Symbol with a descriptor, as
        // it's probably just for tests
        'symbol-description': 'off',
      },
    },
  ],
};