# sort-constructor-parameters

Enforce sorted constructor parameters on classes matching configured conditions.

This rule does not sort constructor parameters by default. It must be configured with [`useConfigurationIf`](#useconfigurationif) to
target only the classes where parameter order does not matter (e.g., classes using dependency injection).

By keeping those constructor parameters sorted, developers can quickly scan and verify the dependencies, making the code more predictable
and reducing the likelihood of errors.

## Try it out

**Initial**

```tsx
@Component({
  selector: 'app-dashboard',
  templateUrl: './dashboard.component.html',
})
export class DashboardComponent {
  constructor(
    private router: Router,
    private analyticsService: AnalyticsService,
    private userService: UserService,
    private authService: AuthService,
  ) {}
}

@Injectable()
export class DataService {
  constructor(
    private httpClient: HttpClient,
    private cacheService: CacheService,
    private loggerService: LoggerService,
  ) {}
}
```

**Sorted alphabetically**

```tsx
@Component({
  selector: 'app-dashboard',
  templateUrl: './dashboard.component.html',
})
export class DashboardComponent {
  constructor(
    private analyticsService: AnalyticsService,
    private authService: AuthService,
    private router: Router,
    private userService: UserService,
  ) {}
}

@Injectable()
export class DataService {
  constructor(
    private cacheService: CacheService,
    private httpClient: HttpClient,
    private loggerService: LoggerService,
  ) {}
}
```

**Sorted by line length**

```tsx
@Component({
  selector: 'app-dashboard',
  templateUrl: './dashboard.component.html',
})
export class DashboardComponent {
  constructor(
    private analyticsService: AnalyticsService,
    private userService: UserService,
    private authService: AuthService,
    private router: Router,
  ) {}
}

@Injectable()
export class DataService {
  constructor(
    private loggerService: LoggerService,
    private cacheService: CacheService,
    private httpClient: HttpClient,
  ) {}
}
```

## Options

This rule accepts an options object with the following properties:

### type

default: `'alphabetical'`

Specifies the sorting method.

- `'alphabetical'` — Sort items alphabetically (e.g., "a" \< "b" \< "c") using [localeCompare](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare).
- `'natural'` — Sort items in a [natural](https://github.com/yobacca/natural-orderby) order (e.g., "item2" \< "item10").
- `'line-length'` — Sort items by code line length (shorter lines first).
- `'custom'` — Sort items using the alphabet specified in the [`alphabet`](#alphabet) option.
- `'unsorted'` — Do not sort items. [`grouping`](#groups) and [`newlines behavior`](#newlinesbetween) are still enforced.

### order

default: `'asc'`

Specifies whether to sort items in ascending or descending order.

- `'asc'` — Sort items in ascending order (A to Z, 1 to 9).
- `'desc'` — Sort items in descending order (Z to A, 9 to 1).

### fallbackSort

type:

```ts
{
  type:
    | 'alphabetical'
    | 'natural'
    | 'line-length'
    | 'custom'
    | 'subgroup-order'
    | 'unsorted'
  order?: 'asc' | 'desc'
}
```

default: `{ type: 'unsorted' }`

Specifies fallback sort options for elements that are equal according to the primary sort [`type`](#type).

You can also sort by subgroup order (nested groups in the [`groups`](#groups) option) using `subgroup-order`.

Example: enforce alphabetical sort between two elements with the same length.

```ts
{
  type: 'line-length',
  order: 'desc',
  fallbackSort: { type: 'alphabetical', order: 'asc' }
}
```

### alphabet

default: `''`

Used only when the [`type`](#type) option is set to `'custom'`. Specifies the custom alphabet for sorting.

Use the `Alphabet` utility class from `eslint-plugin-perfectionist/alphabet` to quickly generate a custom alphabet.

Example: `0123456789abcdef...`

### ignoreCase

default: `true`

Specifies whether sorting should be case-sensitive.

- `true` — Ignore case when sorting alphabetically or naturally (e.g., "A" and "a" are the same).
- `false` — Consider case when sorting (e.g., "a" comes before "A").

### specialCharacters

default: `'keep'`

Specifies whether to trim, remove, or keep special characters before sorting.

- `'keep'` — Keep special characters when sorting (e.g., "\_a" comes before "a").
- `'trim'` — Trim special characters when sorting alphabetically or naturally (e.g., "\_a" and "a" are the same).
- `'remove'` — Remove special characters when sorting (e.g., "/a/b" and "ab" are the same).

### locales

default: `'en-US'`

Specifies the sorting locales. Refer To [String.prototype.localeCompare() - locales](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare#locales).

- `string` — A BCP 47 language tag (e.g. `'en'`, `'en-US'`, `'zh-CN'`).
- `string[]` — An array of BCP 47 language tags.

### partitionByComment

default: `false`

Enables the use of comments to separate the constructor parameters into logical groups. This can help in organizing and maintaining constructors with many parameters by creating partitions based on comments.

- `true` — All comments will be treated as delimiters, creating partitions.
- `false` — Comments will not be used as delimiters.
- `RegExpPattern = string | { pattern: string; flags: string}` — A regexp pattern to specify which comments should act as delimiters.
- `RegExpPattern[]` — A list of regexp patterns to specify which comments should act as delimiters.
- `{ block: boolean | RegExpPattern | RegExpPattern[]; line: boolean | RegExpPattern | RegExpPattern[] }` — Specify which block and line comments should act as delimiters.

### partitionByNewLine

default: `false`

When `true`, the rule will not sort the constructor parameters if there is an empty line between them. This helps maintain the defined order of logically separated groups of parameters.

```ts
constructor(
  // Group 1
  private authService: AuthService,
  private userService: UserService,

  // Group 2
  private logger: LoggerService,
  private router: Router,
) {}
```

Each group of parameters (separated by empty lines) is treated independently, and the order within each group is preserved.

### newlinesBetween

type: `number | 'ignore'`

default: `'ignore'`

Specifies how to handle newlines between groups.

- `'ignore'` — Do not report errors related to newlines.
- `0` — No newlines are allowed.
- Any other number — Enforce this number of newlines between each group.

You can also enforce the newline behavior between two specific groups through the [`groups`](#newlines-between-groups)
option.

This option is only applicable when [`partitionByNewLine`](#partitionbynewline) is `false`.

### newlinesInside

type: `number | 'ignore' | 'newlinesBetween'`

default: `'newlinesBetween'`

Specifies how to handle newlines inside groups.

- `'ignore'` — Do not report errors related to newlines.
- `'newlinesBetween'` — \[DEPRECATED] If [`newlinesBetween`](#newlinesbetween) is `'ignore'`, then `'ignore'`, otherwise `0`.
- `0` — No newlines are allowed.
- Any other number — Enforce this number of newlines between each element of the same group.

You can also enforce the newline behavior inside a given group through the [`groups`](#group-with-overridden-settings)
or [`customGroups`](#customgroups) options.

This option is only applicable when [`partitionByNewLine`](#partitionbynewline) is `false`.

### useConfigurationIf

> **Important**
>
> This option must be explicitly set in each configuration object.

type:

```ts
{
  allNamesMatchPattern?:
    | string
    | string[]
    | { pattern: string; flags: string }
    | { pattern: string; flags: string }[]
  matchesAstSelector?: string
}
```

Specifies filters to match a particular options configuration for a given constructor.

The first matching options configuration will be used. If no configuration matches, the constructor is left unsorted. No fallback configuration is applied.

- `allNamesMatchPattern` — A regexp pattern that all constructor parameter names must match.

- `matchesAstSelector` — An [AST selector](https://eslint.org/docs/latest/extend/selectors) matching a `MethodDefinition` node.
  To avoid unexpected behavior, do not use `:exit` or `:enter` pseudo-selectors.

Example configuration: only sort constructors of Angular components, services, and pipes.

```ts
{
  'perfectionist/sort-constructor-parameters': [
    'error',
    {
      useConfigurationIf: {
        matchesAstSelector: 'ClassDeclaration:has(Decorator[expression.callee.name=/^(Component|Injectable|Pipe)$/]) > ClassBody > MethodDefinition',
      },
      type: 'alphabetical',
    },
  ],
}
```

### groups

type:

```ts
  Array<
    | string
    | string[]
    | { newlinesBetween: number | 'ignore' }
    | {
        group: string | string[];
        type?: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted';
        order?: 'asc' | 'desc';
        fallbackSort?: { type: string; order?: 'asc' | 'desc' };
        newlinesInside?: number | 'ignore';
      }
  >
```

default: `['parameter']`

Specifies a list of groups for sorting. Groups help organize elements into categories.

Each element will be assigned a single group specified in the `groups` option (or the `unknown` group if no match is found).
The order of items in the `groups` option determines how groups are ordered.

Within a given group, members will be sorted according to the `type`, `order`, `ignoreCase`, etc. options.

Individual groups can be combined together by placing them in an array. The order of groups in that array does not matter.
All members of the groups in the array will be sorted together as if they were part of a single group.

Predefined groups are characterized by a selector.

##### Selectors

- `'parameter'` — Constructor parameters that are not rest elements.

**Note:** Rest elements (`...args`) are not sorted and act as partition boundaries. This ensures the original order of rest elements is preserved.

##### Modifiers

Modifiers are listed below by importance, from most to least important:

- `'decorated'` — Matches parameters with at least one decorator.
- `'override'` — Matches parameters declared with the `override` keyword.
- `'readonly'` — Matches parameters declared with the `readonly` keyword.
- `'protected'` — Matches parameters declared with the `protected` keyword.
- `'private'` — Matches parameters declared with the `private` keyword.
- `'public'` — Matches parameters declared with the `public` keyword, or without visibility keyword.

Example: `decorated-readonly-public-parameter`.

#### Important notes

##### Scope of the `public` modifier

Parameters that are neither `protected` nor `private` are matched with the `public` modifier, even if the keyword is absent. This includes plain parameters that are not parameter properties.

##### The `unknown` group

Parameters that don't fit into any group specified in the `groups` option will be placed in the `unknown` group. If the `unknown` group is not specified in the `groups` option, the parameters will remain in their original order.

##### Behavior when multiple groups match a parameter

The list of modifiers above is sorted by importance, from most to least important. When several groups match a parameter, the following rules apply:

1. The group with the most matching modifiers is selected.
2. If the number of matching modifiers is the same, the group is chosen based on modifier importance as listed above.

#### Group with overridden settings

You may directly override options for a specific group by using an object with the `group` property and other option overrides.

- `type` — Overrides the [`type`](#type) option for that group.
- `order` — Overrides the [`order`](#order) option for that group.
- `fallbackSort` — Overrides the [`fallbackSort`](#fallbacksort) option for that group.
- `newlinesInside` — Overrides the [`newlinesInside`](#newlinesinside) option for that group.

```ts
{
  groups: [
    'parameter',
  ]
}
```

#### Newlines between groups

You may place `newlinesBetween` objects between your groups to enforce the newline behavior between two specific groups.

See the [`newlinesBetween`](#newlinesbetween) option.

This feature is only applicable when [`partitionByNewLine`](#partitionbynewline) is `false`.

```ts
{
  newlinesBetween: 1,
  groups: [
    'a',
    { newlinesBetween: 0 }, // Overrides the global newlinesBetween option
    'b',
  ]
}
```

### customGroups

type: `Array<CustomGroupDefinition | CustomGroupAnyOfDefinition>`

default: `[]`

Defines custom groups to match specific constructor parameters.

A custom group definition may follow one of the two following interfaces:

```ts
interface CustomGroupDefinition {
  groupName: string
  type?: 'alphabetical' | 'natural' | 'line-length' | 'unsorted'
  order?: 'asc' | 'desc'
  fallbackSort?: { type: string; order?: 'asc' | 'desc' }
  newlinesInside?: number | 'ignore'
  selector?: string
  modifiers?: string[]
  elementNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
  decoratorNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
}
```

A constructor parameter will match a `CustomGroupDefinition` group if it matches all the filters of the custom group's definition.

or:

```ts
interface CustomGroupAnyOfDefinition {
  groupName: string
  type?: 'alphabetical' | 'natural' | 'line-length' | 'unsorted'
  order?: 'asc' | 'desc'
  fallbackSort?: { type: string; order?: 'asc' | 'desc' }
  newlinesInside?: number | 'ignore'
  anyOf: Array<{
      selector?: string
      modifiers?: string[]
      elementNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
      decoratorNamePattern?: string | string[] | { pattern: string; flags?: string } | { pattern: string; flags?: string }[]
  }>
}
```

A constructor parameter will match a `CustomGroupAnyOfDefinition` group if it matches at least one of the `anyOf` items.

#### Attributes

- `groupName` — The group's name, which needs to be put in the [`groups`](#groups) option.
- `selector` — Filter on the `selector` of the element.
- `modifiers` — Filter on the `modifiers` of the element. (All the modifiers of the element must be present in that list)
- `elementNamePattern` — If entered, will check that the name of the element matches the pattern entered.
- `decoratorNamePattern` — If entered, will check that at least one `decorator` matches the pattern entered.
- `type` — Overrides the [`type`](#type) option for that custom group.
- `order` — Overrides the [`order`](#order) option for that custom group.
- `fallbackSort` — Overrides the [`fallbackSort`](#fallbacksort) option for that custom group.
- `newlinesInside` — Overrides the [`newlinesInside`](#newlinesinside) option for that custom group.

#### Match importance

The `customGroups` list is ordered:
The first custom group definition that matches an element will be used.

Custom groups have a higher priority than any predefined group.

## Usage

**Flat Config**

```tsx
// eslint.config.js
import perfectionist from 'eslint-plugin-perfectionist'

export default [
  {
    plugins: {
      perfectionist,
    },
    rules: {
      'perfectionist/sort-constructor-parameters': [
        'error',
        {
          type: 'alphabetical',
          order: 'asc',
          fallbackSort: { type: 'unsorted' },
          ignoreCase: true,
          specialCharacters: 'keep',
          partitionByNewLine: false,
          newlinesBetween: 'ignore',
          newlinesInside: 'ignore',
          useConfigurationIf: {
            matchesAstSelector: 'ClassDeclaration:has(Decorator[expression.callee.name=/^(Component|Injectable|Pipe)$/]) > ClassBody > MethodDefinition',
          },
          groups: ["parameter"],
          customGroups: [],
        },
      ],
    },
  },
]
```

**Legacy Config**

```tsx
// .eslintrc.js
module.exports = {
  plugins: [
    'perfectionist',
  ],
  rules: {
    'perfectionist/sort-constructor-parameters': [
      'error',
      {
        type: 'alphabetical',
        order: 'asc',
        fallbackSort: { type: 'unsorted' },
        ignoreCase: true,
        specialCharacters: 'keep',
        partitionByNewLine: false,
        newlinesBetween: 'ignore',
        newlinesInside: 'ignore',
        useConfigurationIf: {
          matchesAstSelector: 'ClassDeclaration:has(Decorator[expression.callee.name=/^(Component|Injectable|Pipe)$/]) > ClassBody > MethodDefinition',
        },
        groups: ["parameter"],
        customGroups: [],
      },
    ],
  },
}
```

## Version

This rule was introduced in [v5.13.0](https://github.com/azat-io/eslint-plugin-perfectionist/releases/tag/v5.13.0).

## Resources

- [Rule source](https://github.com/azat-io/eslint-plugin-perfectionist/blob/main/rules/sort-constructor-parameters.ts)
- [Test source](https://github.com/azat-io/eslint-plugin-perfectionist/blob/main/test/rules/sort-constructor-parameters.test.ts)