---
description: 'Disallow magic numbers.'
---

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> 🛑 This file is source code, not the primary documentation location! 🛑
>
> See **https://typescript-eslint.io/rules/no-magic-numbers** for documentation.

It adds support for:

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

## Options

This rule adds the following options:

```ts
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`

{/* insert option description */}

Whether enums used in TypeScript are considered okay. `false` by default.

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

```ts option='{ "ignoreEnums": false }' showPlaygroundButton
enum foo {
  SECOND = 1000,
}
```

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

```ts option='{ "ignoreEnums": true }' showPlaygroundButton
enum foo {
  SECOND = 1000,
}
```

### `ignoreNumericLiteralTypes`

{/* insert option description */}

Whether numbers used in TypeScript numeric literal types are considered okay. `false` by default.

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

```ts option='{ "ignoreNumericLiteralTypes": false }' showPlaygroundButton
type SmallPrimes = 2 | 3 | 5 | 7 | 11;
```

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

```ts option='{ "ignoreNumericLiteralTypes": true }' showPlaygroundButton
type SmallPrimes = 2 | 3 | 5 | 7 | 11;
```

### `ignoreReadonlyClassProperties`

{/* insert option description */}

Whether `readonly` class properties are considered okay.

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

```ts option='{ "ignoreReadonlyClassProperties": false }' showPlaygroundButton
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:

```ts option='{ "ignoreReadonlyClassProperties": true }' showPlaygroundButton
class Foo {
  readonly A = 1;
  readonly B = 2;
  public static readonly C = 1;
  static readonly D = 1;
}
```

### `ignoreTypeIndexes`

{/* insert option description */}

Whether numbers used to index types are okay. `false` by default.

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

```ts option='{ "ignoreTypeIndexes": false }' showPlaygroundButton
type Foo = Bar[0];
type Baz = Parameters<Foo>[2];
```

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

```ts option='{ "ignoreTypeIndexes": true }' showPlaygroundButton
type Foo = Bar[0];
type Baz = Parameters<Foo>[2];
```

## When Not To Use It

If your project frequently deals with constant numbers and you don't wish to take up extra space to declare them, this rule might not be for you.
We recommend at least using descriptive comments and/or names to describe constants.
You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#use-configuration-comments) instead of completely disabling this rule.
