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sort-type-constituents

Enforce constituents of a type union/intersection to be sorted alphabetically.

🔧

Some problems reported by this rule are automatically fixable by the --fix ESLint command line option.

💡

Some problems reported by this rule are manually fixable by editor suggestions.

Sorting union (|) and intersection (&) types can help:

  • keep your codebase standardized
  • find repeated types
  • reduce diff churn

This rule reports on any types that aren't sorted alphabetically.

Types are sorted case-insensitively and treating numbers like a human would, falling back to character code sorting in case of ties.

note

This rule is feature frozen: it will no longer receive new features such as new options. It still will accept bug and documentation fixes for its existing area of features.

Stylistic rules that enforce naming and/or sorting conventions tend to grow incomprehensibly complex as increasingly obscure features are requested. This rule has reached the limit of what is reasonable for the typescript-eslint project to maintain. See eslint-plugin: Feature freeze naming and sorting stylistic rules for more information.

.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/sort-type-constituents": "error"
  }
};

Try this rule in the playground ↗

Examples​

type T1 = B | A;

type T2 = { b: string } & { a: string };

type T3 = [1, 2, 4] & [1, 2, 3];

type T4 =
  | [1, 2, 4]
  | [1, 2, 3]
  | { b: string }
  | { a: string }
  | (() => void)
  | (() => string)
  | 'b'
  | 'a'
  | 'b'
  | 'a'
  | readonly string[]
  | readonly number[]
  | string[]
  | number[]
  | B
  | A
  | string
  | any;
Open in Playground

Options​

This rule accepts the following options:

type Options = [
  {
    /** Whether to check intersection types. */
    checkIntersections?: boolean;
    /** Whether to check union types. */
    checkUnions?: boolean;
    /** Ordering of the groups. */
    groupOrder?: (
      | 'conditional'
      | 'function'
      | 'import'
      | 'intersection'
      | 'keyword'
      | 'literal'
      | 'named'
      | 'nullish'
      | 'object'
      | 'operator'
      | 'tuple'
      | 'union'
    )[];
  },
];

const defaultOptions: Options = [
  {
    checkIntersections: true,
    checkUnions: true,
    groupOrder: [
      'named',
      'keyword',
      'operator',
      'literal',
      'function',
      'import',
      'conditional',
      'object',
      'tuple',
      'intersection',
      'union',
      'nullish',
    ],
  },
];

checkIntersections​

Whether to check intersection types (&).

Examples of code with { "checkIntersections": true } (the default):

type ExampleIntersection = B & A;
Open in Playground

checkUnions​

Whether to check union types (|).

Examples of code with { "checkUnions": true } (the default):

type ExampleUnion = B | A;
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groupOrder​

Each constituent of the type is placed into a group, and then the rule sorts alphabetically within each group. The ordering of groups is determined by this option.

  • conditional - Conditional types (A extends B ? C : D)
  • function - Function and constructor types (() => void, new () => type)
  • import - Import types (import('path'))
  • intersection - Intersection types (A & B)
  • keyword - Keyword types (any, string, etc)
  • literal - Literal types (1, 'b', true, etc)
  • named - Named types (A, A['prop'], B[], Array<C>)
  • object - Object types ({ a: string }, { [key: string]: number })
  • operator - Operator types (keyof A, typeof B, readonly C[])
  • tuple - Tuple types ([A, B, C])
  • union - Union types (A | B)
  • nullish - null and undefined

For example, configuring the rule with { "groupOrder": ["literal", "nullish" ]}:

type ExampleGroup = null | 123;
Open in Playground

When Not To Use It​

This rule is purely a stylistic rule for maintaining consistency in your project. You can turn it off if you don't want to keep a consistent, predictable order for intersection and union types. However, keep in mind that inconsistent style can harm readability in a project.

Resources​