member-delimiter-style

Require a specific member delimiter style for interfaces and type literals.

Enforces a consistent member delimiter style in interfaces and type literals. There are three member delimiter styles primarily used in TypeScript:

• Semicolon style (default, preferred in TypeScript).

interface Foo {
    name: string;
    greet(): void;
}

type Bar = {
    name: string;
    greet(): void;
}

• Comma style (JSON style).

interface Foo {
    name: string,
    greet(): void,
}

type Bar = {
    name: string,
    greet(): void,
}

• Line break (none) style.

interface Foo {
    name: string
    greet(): void
}

type Bar = {
    name: string
    greet(): void
}

The rule also enforces the presence (or absence) of the delimiter in the last member of the interface and/or type literal. Finally, this rule can enforce separate delimiter syntax for single line declarations.

Attributes

• Included in configs
  • ✅ Recommended
  • 🔒 Strict
• Fixable
  • 🔧 Automated Fixer
  • 🛠 Suggestion Fixer
• 💭 Requires type information

Rule Details

This rule aims to standardize the way interface and type literal members are delimited.

Options

interface BaseConfig {
  multiline?: {
    delimiter?: 'none' | 'semi' | 'comma';
    requireLast?: boolean;
  };
  singleline?: {
    delimiter?: 'semi' | 'comma';
    requireLast?: boolean;
  };
}
type Config = BaseConfig & {
  overrides?: {
    interface?: BaseConfig;
    typeLiteral?: BaseConfig;
  };
  multilineDetection?: 'brackets' | 'last-member';
};

Default config:

{
  "multiline": {
    "delimiter": "semi",
    "requireLast": true
  },
  "singleline": {
    "delimiter": "semi",
    "requireLast": false
  },
  "multilineDetection": "brackets"
}

multiline config only applies to multiline interface/type definitions. singleline config only applies to single line interface/type definitions. The two configs are entirely separate, and do not effect one another.

multilineDetection determines what counts as multiline

• "brackets" (default) any newlines in the type or interface make it multiline.
• "last-member" if the last member of the interface is on the same line as the last bracket, it is counted as a single line.

delimiter

Accepts three values (or two for singleline):

• comma - each member should be delimited with a comma (,).
• semi - each member should be delimited with a semicolon (;).
• none - each member should be delimited with nothing.

note

none is not an option for singleline because having no delimiter between members on a single line is a syntax error in TS.

requireLast

Determines whether or not the last member in the interface/type should have a delimiter:

• true - the last member must have a delimiter.
• false - the last member must not have a delimiter.

overrides

Allows you to specify options specifically for either interfaces or type definitions / inline types.

For example, to require commas for types, and semicolons for multiline interfaces:

{
  "multiline": {
    "delimiter": "comma",
    "requireLast": true
  },
  "singleline": {
    "delimiter": "comma",
    "requireLast": true
  },
  "overrides": {
    "interface": {
      "multiline": {
        "delimiter": "semi",
        "requireLast": true
      }
    }
  }
}

Examples

Examples of code for this rule with the default config:

❌ Incorrect

// missing semicolon delimiter
interface Foo {
    name: string
    greet(): string
}

// using incorrect delimiter
interface Bar {
    name: string,
    greet(): string,
}

// missing last member delimiter
interface Baz {
    name: string;
    greet(): string
}

// incorrect delimiter
type FooBar = { name: string, greet(): string }

// last member should not have delimiter
type FooBar = { name: string; greet(): string; }

✅ Correct

interface Foo {
    name: string;
    greet(): string;
}

interface Foo { name: string }

type Bar = {
    name: string;
    greet(): string;
}

type Bar = { name: string }

type FooBar = { name: string; greet(): string }

When Not To Use It

If you don't care about enforcing a consistent member delimiter in interfaces and type literals, then you will not need this rule.