no-magic-numbers.md

Disallow Magic Numbers (@typescript-eslint/no-magic-numbers)

'Magic numbers' are numbers that occur multiple times in code without an explicit meaning. They should preferably be replaced by named constants.

Rule Details

The @typescript-eslint/no-magic-numbers rule extends the no-magic-numbers rule from ESLint core, and adds support for handling Typescript specific code that would otherwise trigger the rule.

See the ESLint documentation for more details on the no-magic-numbers rule.

Rule Changes

{
    // note you must disable the base rule as it can report incorrect errors
    "no-magic-numbers": "off",
    "@typescript-eslint/no-magic-numbers": ["error", { "ignoreNumericLiteralTypes": true }]
}

In addition to the options supported by the no-magic-numbers rule in ESLint core, the rule adds the following options:

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;
}

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,
}

^{Taken with ❤️ from ESLint core}