no-magic-numbers

Disallow magic numbers.

Examples

This rule extends the base eslint/no-magic-numbers rule. It adds support for:

• numeric literal types (type T = 1),
• enum members (enum Foo { bar = 1 }),
• readonly class properties (class Foo { readonly bar = 1 }).

How to Use

.eslintrc.cjs

module.exports = {
  "rules": {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-magic-numbers": "off",
    "@typescript-eslint/no-magic-numbers": "error"
  }
};

Try this rule in the playground ↗

Options

See eslint/no-magic-numbers options.

This rule adds the following options:

interface Options extends BaseNoMagicNumbersOptions {
  ignoreEnums?: boolean;
  ignoreNumericLiteralTypes?: boolean;
  ignoreReadonlyClassProperties?: boolean;
  ignoreTypeIndexes?: boolean;
}

const defaultOptions: Options = {
  ...baseNoMagicNumbersDefaultOptions,
  ignoreEnums: false,
  ignoreNumericLiteralTypes: false,
  ignoreReadonlyClassProperties: false,
  ignoreTypeIndexes: false,
};

ignoreEnums

A boolean to specify if enums used in TypeScript are considered okay. false by default.

Examples of incorrect code for the { "ignoreEnums": false } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreEnums": false }]*/

enum foo {
  SECOND = 1000,
}

Examples of correct code for the { "ignoreEnums": true } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreEnums": true }]*/

enum foo {
  SECOND = 1000,
}

ignoreNumericLiteralTypes

A boolean to specify if numbers used in TypeScript numeric literal types are considered okay. false by default.

Examples of incorrect code for the { "ignoreNumericLiteralTypes": false } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreNumericLiteralTypes": false }]*/

type SmallPrimes = 2 | 3 | 5 | 7 | 11;

Examples of correct code for the { "ignoreNumericLiteralTypes": true } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreNumericLiteralTypes": true }]*/

type SmallPrimes = 2 | 3 | 5 | 7 | 11;

ignoreReadonlyClassProperties

Examples of incorrect code for the { "ignoreReadonlyClassProperties": false } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreReadonlyClassProperties": false }]*/

class Foo {
  readonly A = 1;
  readonly B = 2;
  public static readonly C = 1;
  static readonly D = 1;
}

Examples of correct code for the { "ignoreReadonlyClassProperties": true } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreReadonlyClassProperties": true }]*/

class Foo {
  readonly A = 1;
  readonly B = 2;
  public static readonly C = 1;
  static readonly D = 1;
}

ignoreTypeIndexes

A boolean to specify if numbers used to index types are okay. false by default.

Examples of incorrect code for the { "ignoreTypeIndexes": false } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreTypeIndexes": false }]*/

type Foo = Bar[0];
type Baz = Parameters<Foo>[2];

Examples of correct code for the { "ignoreTypeIndexes": true } option:

/*eslint @typescript-eslint/no-magic-numbers: ["error", { "ignoreTypeIndexes": true }]*/

type Foo = Bar[0];
type Baz = Parameters<Foo>[2];

Resources

• Rule source
• Test source

^{Taken with ❤️ from ESLint core}