eslint-config-ts-strict/rules/best-practices.js

Very strict ESLint config for projects using TypeScript, React and Prettier. ESLint v9 flat config only. Formatting rules disabled to prevent Prettier conflicts.

export default {
  rules: {
    // enforces getter/setter pairs in objects
    // https://eslint.org/docs/rules/accessor-pairs
    "accessor-pairs": "off",

    // enforces return statements in callbacks of array's methods
    // https://eslint.org/docs/rules/array-callback-return
    "array-callback-return": ["error", { allowImplicit: true }],

    // treat var statements as if they were block scoped
    // https://eslint.org/docs/rules/block-scoped-var
    "block-scoped-var": "error",

    // https://eslint.org/docs/latest/rules/camelcase
    camelcase: ["off", { properties: "never" }],

    // specify the maximum cyclomatic complexity allowed in a program
    // https://eslint.org/docs/rules/complexity
    complexity: ["off", 20],

    // enforce that class methods use "this"
    // https://eslint.org/docs/rules/class-methods-use-this
    "class-methods-use-this": [
      "off",
      {
        exceptMethods: [],
      },
    ],

    // require return statements to either always or never specify values
    // https://eslint.org/docs/rules/consistent-return
    "consistent-return": "off",
    "@typescript-eslint/consistent-return": "error",

    // specify curly brace conventions for all control statements
    // https://eslint.org/docs/rules/curly
    curly: ["error", "multi-line"], // multiline

    // require default case in switch statements
    // https://eslint.org/docs/rules/default-case
    "default-case": ["error", { commentPattern: "^no default$" }],

    // Enforce default clauses in switch statements to be last
    // https://eslint.org/docs/rules/default-case-last
    "default-case-last": "error",

    // enforces consistent newlines before or after dots
    // https://eslint.org/docs/rules/dot-location
    "dot-location": ["error", "property"],

    // require the use of === and !==
    // https://eslint.org/docs/rules/eqeqeq
    eqeqeq: ["error", "always", { null: "ignore" }],

    // Require grouped accessor pairs in object literals and classes
    // https://eslint.org/docs/rules/grouped-accessor-pairs
    "grouped-accessor-pairs": "error",

    // make sure for-in loops have an if statement
    // https://eslint.org/docs/rules/guard-for-in
    "guard-for-in": "error",

    // https://eslint.org/docs/latest/rules/logical-assignment-operators
    "logical-assignment-operators": [
      "error",
      "always",
      { enforceForIfStatements: true },
    ],

    // enforce a maximum number of classes per file
    // https://eslint.org/docs/rules/max-classes-per-file
    "max-classes-per-file": "off",

    // disallow the use of alert, confirm, and prompt
    // https://eslint.org/docs/rules/no-alert
    "no-alert": "warn",

    // disallow use of arguments.caller or arguments.callee
    // https://eslint.org/docs/rules/no-caller
    "no-caller": "error",

    // disallow lexical declarations in case/default clauses
    // https://eslint.org/docs/rules/no-case-declarations
    "no-case-declarations": "error",

    // https://eslint.org/docs/latest/rules/no-constant-binary-expression
    "no-constant-binary-expression": "error",

    // Disallow returning value in constructor
    // https://eslint.org/docs/rules/no-constructor-return
    "no-constructor-return": "error",

    // disallow division operators explicitly at beginning of regular expression
    // https://eslint.org/docs/rules/no-div-regex
    "no-div-regex": "off",

    // disallow else after a return in an if
    // https://eslint.org/docs/rules/no-else-return
    "no-else-return": ["error", { allowElseIf: false }],

    // disallow empty destructuring patterns
    // https://eslint.org/docs/rules/no-empty-pattern
    "no-empty-pattern": "error",

    // disallow comparisons to null without a type-checking operator
    // https://eslint.org/docs/rules/no-eq-null
    "no-eq-null": "off",

    // disallow use of eval()
    // https://eslint.org/docs/rules/no-eval
    "no-eval": "error",

    // disallow adding to native types
    // https://eslint.org/docs/rules/no-extend-native
    "no-extend-native": "error",

    // disallow unnecessary function binding
    // https://eslint.org/docs/rules/no-extra-bind
    "no-extra-bind": "error",

    // disallow Unnecessary Labels
    // https://eslint.org/docs/rules/no-extra-label
    "no-extra-label": "error",

    // disallow fallthrough of case statements
    // https://eslint.org/docs/rules/no-fallthrough
    "no-fallthrough": "error",

    // disallow the use of leading or trailing decimal points in numeric literals
    // https://eslint.org/docs/rules/no-floating-decimal
    "no-floating-decimal": "error",

    // disallow reassignments of native objects or read-only globals
    // https://eslint.org/docs/rules/no-global-assign
    "no-global-assign": ["error", { exceptions: [] }],

    // deprecated in favor of no-global-assign
    // https://eslint.org/docs/rules/no-native-reassign
    "no-native-reassign": "off",

    // disallow implicit type conversions
    // https://eslint.org/docs/rules/no-implicit-coercion
    "no-implicit-coercion": [
      "off",
      {
        boolean: false,
        number: true,
        string: true,
        allow: [],
      },
    ],

    // disallow var and named functions in global scope
    // https://eslint.org/docs/rules/no-implicit-globals
    "no-implicit-globals": "off",

    // disallow usage of __iterator__ property
    // https://eslint.org/docs/rules/no-iterator
    "no-iterator": "error",

    // disallow use of labels for anything other than loops and switches
    // https://eslint.org/docs/rules/no-labels
    "no-labels": ["error", { allowLoop: false, allowSwitch: false }],

    // disallow unnecessary nested blocks
    // https://eslint.org/docs/rules/no-lone-blocks
    "no-lone-blocks": "error",

    // disallow use of multiple spaces
    // https://eslint.org/docs/rules/no-multi-spaces
    // PRETTIER CONFLICT: This rule conflicts with Prettier's spacing decisions
    "no-multi-spaces": "off",

    // disallow use of multiline strings
    // https://eslint.org/docs/rules/no-multi-str
    "no-multi-str": "error",

    // disallow use of new operator when not part of the assignment or comparison
    // https://eslint.org/docs/rules/no-new
    "no-new": "error",

    // https://eslint.org/docs/latest/rules/no-new-func
    "no-new-func": "error",

    // disallows creating new instances of String, Number, and Boolean
    // https://eslint.org/docs/rules/no-new-wrappers
    "no-new-wrappers": "error",

    // Disallow \8 and \9 escape sequences in string literals
    // https://eslint.org/docs/rules/no-nonoctal-decimal-escape
    "no-nonoctal-decimal-escape": "error",

    // disallow use of (old style) octal literals
    // https://eslint.org/docs/rules/no-octal
    "no-octal": "error",

    // disallow use of octal escape sequences in string literals, such as
    // var foo = 'Copyright \251';
    // https://eslint.org/docs/rules/no-octal-escape
    "no-octal-escape": "error",

    // disallow reassignment of function parameters
    // disallow parameter object manipulation except for specific exclusions
    // rule: https://eslint.org/docs/rules/no-param-reassign.html
    "no-param-reassign": [
      "error",
      {
        props: true,
        ignorePropertyModificationsFor: [
          "acc", // for reduce accumulators
          "accumulator", // for reduce accumulators
          "e", // for e.returnvalue
          "ctx", // for Koa routing
          "context", // for Koa routing
          "req", // for Express requests
          "request", // for Express requests
          "res", // for Express responses
          "response", // for Express responses
          "$scope", // for Angular 1 scopes
          "staticContext", // for ReactRouter context
        ],
      },
    ],

    // disallow usage of __proto__ property
    // https://eslint.org/docs/rules/no-proto
    "no-proto": "error",

    // disallow certain object properties
    // https://eslint.org/docs/rules/no-restricted-properties
    "no-restricted-properties": [
      "error",
      {
        object: "arguments",
        property: "callee",
        message: "arguments.callee is deprecated",
      },
      {
        object: "global",
        property: "isFinite",
        message: "Please use Number.isFinite instead",
      },
      {
        object: "self",
        property: "isFinite",
        message: "Please use Number.isFinite instead",
      },
      {
        object: "window",
        property: "isFinite",
        message: "Please use Number.isFinite instead",
      },
      {
        object: "global",
        property: "isNaN",
        message: "Please use Number.isNaN instead",
      },
      {
        object: "self",
        property: "isNaN",
        message: "Please use Number.isNaN instead",
      },
      {
        object: "window",
        property: "isNaN",
        message: "Please use Number.isNaN instead",
      },
      {
        property: "__defineGetter__",
        message: "Please use Object.defineProperty instead.",
      },
      {
        property: "__defineSetter__",
        message: "Please use Object.defineProperty instead.",
      },
      {
        object: "Math",
        property: "pow",
        message: "Use the exponentiation operator (**) instead.",
      },
    ],

    // disallow use of assignment in return statement
    // https://eslint.org/docs/rules/no-return-assign
    "no-return-assign": ["error", "always"],

    // disallow use of `javascript:` urls.
    // https://eslint.org/docs/rules/no-script-url
    "no-script-url": "error",

    // disallow self assignment
    // https://eslint.org/docs/rules/no-self-assign
    "no-self-assign": [
      "error",
      {
        props: true,
      },
    ],

    // disallow comparisons where both sides are exactly the same
    // https://eslint.org/docs/rules/no-self-compare
    "no-self-compare": "error",

    // disallow use of comma operator
    // https://eslint.org/docs/rules/no-sequences
    "no-sequences": "error",

    // disallow unmodified conditions of loops
    // https://eslint.org/docs/rules/no-unmodified-loop-condition
    "no-unmodified-loop-condition": "off",

    // disallow unused labels
    // https://eslint.org/docs/rules/no-unused-labels
    "no-unused-labels": "error",

    // disallow unnecessary .call() and .apply()
    // https://eslint.org/docs/rules/no-useless-call
    "no-useless-call": "off",

    // Disallow unnecessary catch clauses
    // https://eslint.org/docs/rules/no-useless-catch
    "no-useless-catch": "error",

    // disallow useless string concatenation
    // https://eslint.org/docs/rules/no-useless-concat
    "no-useless-concat": "error",

    // disallow unnecessary string escaping
    // https://eslint.org/docs/rules/no-useless-escape
    "no-useless-escape": "error",

    // disallow redundant return; keywords
    // https://eslint.org/docs/rules/no-useless-return
    "no-useless-return": "error",

    // disallow use of void operator
    // https://eslint.org/docs/rules/no-void
    "no-void": "error",

    // disallow usage of configurable warning terms in comments: e.g. todo
    // https://eslint.org/docs/rules/no-warning-comments
    "no-warning-comments": [
      "off",
      { terms: ["todo", "fixme", "xxx"], location: "start" },
    ],

    // disallow use of the with statement
    // https://eslint.org/docs/rules/no-with
    "no-with": "error",

    // require using Error objects as Promise rejection reasons
    // https://eslint.org/docs/rules/prefer-promise-reject-errors
    "prefer-promise-reject-errors": ["error", { allowEmptyReject: true }],

    // Suggest using named capture group in regular expression
    // https://eslint.org/docs/rules/prefer-named-capture-group
    "prefer-named-capture-group": "off",

    // https://eslint.org/docs/latest/rules/prefer-object-has-own
    "prefer-object-has-own": "error",

    // https://eslint.org/docs/rules/prefer-regex-literals
    "prefer-regex-literals": [
      "error",
      {
        disallowRedundantWrapping: true,
      },
    ],

    // require use of the second argument for parseInt()
    // https://eslint.org/docs/rules/radix
    radix: "error",

    // Enforce the use of u flag on RegExp
    // https://eslint.org/docs/rules/require-unicode-regexp
    "require-unicode-regexp": "off",

    // requires to declare all vars on top of their containing scope
    // https://eslint.org/docs/rules/vars-on-top
    "vars-on-top": "error",

    // require immediate function invocation to be wrapped in parentheses
    // https://eslint.org/docs/rules/wrap-iife.html
    "wrap-iife": ["error", "outside", { functionPrototypeMethods: false }],

    // require or disallow Yoda conditions
    // https://eslint.org/docs/rules/yoda
    yoda: "error",

    "no-object-constructor": "error",
  },
};