naming-convention

Enforce naming conventions for everything across a codebase.

💭

This rule requires type information to run.

Enforcing naming conventions helps keep the codebase consistent, and reduces overhead when thinking about how to name a variable. Additionally, a well-designed style guide can help communicate intent, such as by enforcing all private properties begin with an _, and all global-level constants are written in UPPER_CASE.

.eslintrc.cjs

module.exports = {
  "rules": {
    "@typescript-eslint/naming-convention": "warn"
  }
};

Examples

This rule allows you to enforce conventions for any identifier, using granular selectors to create a fine-grained style guide.

note

This rule only needs type information in specific cases, detailed below.

Options

This rule accepts an array of objects, with each object describing a different naming convention. Each property will be described in detail below. Also see the examples section below for illustrated examples.

type Options = {
  // format options
  format:
    | (
        | 'camelCase'
        | 'strictCamelCase'
        | 'PascalCase'
        | 'StrictPascalCase'
        | 'snake_case'
        | 'UPPER_CASE'
      )[]
    | null;
  custom?: {
    regex: string;
    match: boolean;
  };
  leadingUnderscore?:
    | 'forbid'
    | 'require'
    | 'requireDouble'
    | 'allow'
    | 'allowDouble'
    | 'allowSingleOrDouble';
  trailingUnderscore?:
    | 'forbid'
    | 'require'
    | 'requireDouble'
    | 'allow'
    | 'allowDouble'
    | 'allowSingleOrDouble';
  prefix?: string[];
  suffix?: string[];

  // selector options
  selector: Selector | Selector[];
  filter?:
    | string
    | {
        regex: string;
        match: boolean;
      };
  // the allowed values for these are dependent on the selector - see below
  modifiers?: Modifiers<Selector>[];
  types?: Types<Selector>[];
}[];

// the default config is similar to ESLint's camelcase rule but more strict
const defaultOptions: Options = [
  {
    selector: 'default',
    format: ['camelCase'],
    leadingUnderscore: 'allow',
    trailingUnderscore: 'allow',
  },

  {
    selector: 'variable',
    format: ['camelCase', 'UPPER_CASE'],
    leadingUnderscore: 'allow',
    trailingUnderscore: 'allow',
  },

  {
    selector: 'typeLike',
    format: ['PascalCase'],
  },
];

Format Options

Every single selector can have the same set of format options. For information about how each selector is applied, see "How does the rule evaluate a name's format?".

format

The format option defines the allowed formats for the identifier. This option accepts an array of the following values, and the identifier can match any of them:

• camelCase - standard camelCase format - no underscores are allowed between characters, and consecutive capitals are allowed (i.e. both myID and myId are valid).
• strictCamelCase - same as camelCase, but consecutive capitals are not allowed (i.e. myId is valid, but myID is not).
• PascalCase - same as camelCase, except the first character must be upper-case.
• StrictPascalCase - same as strictCamelCase, except the first character must be upper-case.
• snake_case - standard snake_case format - all characters must be lower-case, and underscores are allowed.
• UPPER_CASE - same as snake_case, except all characters must be upper-case.

Instead of an array, you may also pass null. This signifies "this selector shall not have its format checked". This can be useful if you want to enforce no particular format for a specific selector, after applying a group selector.

custom

The custom option defines a custom regex that the identifier must (or must not) match. This option allows you to have a bit more finer-grained control over identifiers, letting you ban (or force) certain patterns and substrings. Accepts an object with the following properties:

• regex - a string that is then passed into RegExp to create a new regular expression: new RegExp(regex)
• match - true if the identifier must match the regex, false if the identifier must not match the regex.

filter

The filter option operates similar to custom, accepting the same shaped object, except that it controls if the rest of the configuration should or should not be applied to an identifier.

You can use this to include or exclude specific identifiers from specific configurations.

Accepts an object with the following properties:

• regex - a string that is then passed into RegExp to create a new regular expression: new RegExp(regex)
• match - true if the identifier must match the regex, false if the identifier must not match the regex.

Alternatively, filter accepts a regular expression (anything accepted into new RegExp(filter)). In this case, it's treated as if you had passed an object with the regex and match: true.

leadingUnderscore / trailingUnderscore

The leadingUnderscore / trailingUnderscore options control whether leading/trailing underscores are considered valid. Accepts one of the following values:

• forbid - a leading/trailing underscore is not allowed at all.
• require - a single leading/trailing underscore must be included.
• requireDouble - two leading/trailing underscores must be included.
• allow - existence of a single leading/trailing underscore is not explicitly enforced.
• allowDouble - existence of a double leading/trailing underscore is not explicitly enforced.
• allowSingleOrDouble - existence of a single or a double leading/trailing underscore is not explicitly enforced.

prefix / suffix

The prefix / suffix options control which prefix/suffix strings must exist for the identifier. Accepts an array of strings.

If these are provided, the identifier must start with one of the provided values. For example, if you provide { prefix: ['IFace', 'Class', 'Type'] }, then the following names are valid: IFaceFoo, ClassBar, TypeBaz, but the name Bang is not valid, as it contains none of the prefixes.

Note: As documented above, the prefix is trimmed before format is validated, therefore PascalCase must be used to allow variables such as isEnabled using the prefix is.

Selector Options

• selector allows you to specify what types of identifiers to target.
  • Accepts one or array of selectors to define an option block that applies to one or multiple selectors.
  • For example, if you provide { selector: ['variable', 'function'] }, then it will apply the same option to variable and function nodes.
  • See Allowed Selectors, Modifiers and Types below for the complete list of allowed selectors.
• modifiers allows you to specify which modifiers to granularly apply to, such as the accessibility (private/public/protected), or if the thing is static, etc.
  • The name must match all of the modifiers.
  • For example, if you provide { modifiers: ['private', 'static', 'readonly'] }, then it will only match something that is private static readonly, and something that is just private will not match.
  • The following modifiers are allowed:
    • const - matches a variable declared as being const (const x = 1).
    • destructured - matches a variable declared via an object destructuring pattern (const {x, z = 2}).
      • Note that this does not match renamed destructured properties (const {x: y, a: b = 2}).
    • global - matches a variable/function declared in the top-level scope.
    • exported - matches anything that is exported from the module.
    • unused - matches anything that is not used.
    • requiresQuotes - matches any name that requires quotes as it is not a valid identifier (i.e. has a space, a dash, etc in it).
    • public - matches any member that is either explicitly declared as public, or has no visibility modifier (i.e. implicitly public).
    • readonly, static, abstract, protected, private - matches any member explicitly declared with the given modifier.
• types allows you to specify which types to match. This option supports simple, primitive types only (boolean, string, number, array, function).
  • The name must match one of the types.
  • NOTE - Using this option will require that you lint with type information.
  • For example, this lets you do things like enforce that boolean variables are prefixed with a verb.
  • The following types are allowed:
    • boolean matches any type assignable to boolean | null | undefined
    • string matches any type assignable to string | null | undefined
    • number matches any type assignable to number | null | undefined
    • array matches any type assignable to Array<unknown> | null | undefined
    • function matches any type assignable to Function | null | undefined

The ordering of selectors does not matter. The implementation will automatically sort the selectors to ensure they match from most-specific to least specific. It will keep checking selectors in that order until it finds one that matches the name. See "How does the rule automatically order selectors?"

Allowed Selectors, Modifiers and Types

There are two types of selectors, individual selectors, and grouped selectors.

Individual Selectors

Individual Selectors match specific, well-defined sets. There is no overlap between each of the individual selectors.

• variable - matches any var / let / const variable name.
  • Allowed modifiers: const, destructured, global, exported, unused.
  • Allowed types: boolean, string, number, function, array.
• function - matches any named function declaration or named function expression.
  • Allowed modifiers: global, exported, unused.
  • Allowed types: none.
• parameter - matches any function parameter. Does not match parameter properties.
  • Allowed modifiers: destructured, unused.
  • Allowed types: boolean, string, number, function, array.
• classProperty - matches any class property. Does not match properties that have direct function expression or arrow function expression values.
  • Allowed modifiers: abstract, private, protected, public, readonly, requiresQuotes, static.
  • Allowed types: boolean, string, number, function, array.
• objectLiteralProperty - matches any object literal property. Does not match properties that have direct function expression or arrow function expression values.
  • Allowed modifiers: public, requiresQuotes.
  • Allowed types: boolean, string, number, function, array.
• typeProperty - matches any object type property. Does not match properties that have direct function expression or arrow function expression values.
  • Allowed modifiers: public, readonly, requiresQuotes.
  • Allowed types: boolean, string, number, function, array.
• parameterProperty - matches any parameter property.
  • Allowed modifiers: private, protected, public, readonly.
  • Allowed types: boolean, string, number, function, array.
• classMethod - matches any class method. Also matches properties that have direct function expression or arrow function expression values. Does not match accessors.
  • Allowed modifiers: abstract, private, protected, public, requiresQuotes, static.
  • Allowed types: none.
• objectLiteralMethod - matches any object literal method. Also matches properties that have direct function expression or arrow function expression values. Does not match accessors.
  • Allowed modifiers: public, requiresQuotes.
  • Allowed types: none.
• typeMethod - matches any object type method. Also matches properties that have direct function expression or arrow function expression values. Does not match accessors.
  • Allowed modifiers: public, requiresQuotes.
  • Allowed types: none.
• accessor - matches any accessor.
  • Allowed modifiers: abstract, private, protected, public, requiresQuotes, static.
  • Allowed types: boolean, string, number, function, array.
• enumMember - matches any enum member.
  • Allowed modifiers: requiresQuotes.
  • Allowed types: none.
• class - matches any class declaration.
  • Allowed modifiers: abstract, exported, unused.
  • Allowed types: none.
• interface - matches any interface declaration.
  • Allowed modifiers: exported, unused.
  • Allowed types: none.
• typeAlias - matches any type alias declaration.
  • Allowed modifiers: exported, unused.
  • Allowed types: none.
• enum - matches any enum declaration.
  • Allowed modifiers: exported, unused.
  • Allowed types: none.
• typeParameter - matches any generic type parameter declaration.
  • Allowed modifiers: unused.
  • Allowed types: none.

Group Selectors

Group Selectors are provided for convenience, and essentially bundle up sets of individual selectors.

• default - matches everything.
  • Allowed modifiers: all modifiers.
  • Allowed types: none.
• variableLike - matches the same as variable, function and parameter.
  • Allowed modifiers: unused.
  • Allowed types: none.
• memberLike - matches the same as property, parameterProperty, method, accessor, enumMember.
  • Allowed modifiers: private, protected, public, static, readonly, abstract, requiresQuotes.
  • Allowed types: none.
• typeLike - matches the same as class, interface, typeAlias, enum, typeParameter.
  • Allowed modifiers: abstract, unused.
  • Allowed types: none.
• property - matches the same as classProperty, objectLiteralProperty, typeProperty.
  • Allowed modifiers: private, protected, public, static, readonly, abstract, requiresQuotes.
  • Allowed types: boolean, string, number, function, array.
• method - matches the same as classMethod, objectLiteralMethod, typeMethod.
  • Allowed modifiers: private, protected, public, static, readonly, abstract, requiresQuotes.
  • Allowed types: none.

FAQ

This is a big rule, and there's a lot of docs. Here are a few clarifications that people often ask about or figure out via trial-and-error.

How does the rule evaluate a selector?

Each selector is checked in the following way:

1. check the selector
   1. if selector is one individual selector → the name's type must be of that type.
   2. if selector is a group selector → the name's type must be one of the grouped types.
   3. if selector is an array of selectors → apply the above for each selector in the array.
2. check the filter
   1. if filter is omitted → skip this step.
   2. if the name matches the filter → continue evaluating this selector.
   3. if the name does not match the filter → skip this selector and continue to the next selector.
3. check the types
   1. if types is omitted → skip this step.
   2. if the name has a type in types → continue evaluating this selector.
   3. if the name does not have a type in types → skip this selector and continue to the next selector.

A name is considered to pass the config if it:

1. Matches one selector and passes all of that selector's format checks.
2. Matches no selectors.

A name is considered to fail the config if it matches one selector and fails one that selector's format checks.

How does the rule automatically order selectors?

Each identifier should match exactly one selector. It may match multiple group selectors - but only ever one selector. With that in mind - the base sort order works out to be:

1. Individual Selectors
2. Grouped Selectors
3. Default Selector

Within each of these categories, some further sorting occurs based on what selector options are supplied:

1. filter is given the highest priority above all else.
2. types
3. modifiers
4. everything else

For example, if you provide the following config:

[
  /* 1 */ { selector: 'default', format: ['camelCase'] },
  /* 2 */ { selector: 'variable', format: ['snake_case'] },
  /* 3 */ { selector: 'variable', types: ['boolean'], format: ['UPPER_CASE'] },
  /* 4 */ { selector: 'variableLike', format: ['PascalCase'] },
];

Then for the code const x = 1, the rule will validate the selectors in the following order: 3, 2, 4, 1. To clearly spell it out:

• (3) is tested first because it has types and is an individual selector.
• (2) is tested next because it is an individual selector.
• (4) is tested next as it is a grouped selector.
• (1) is tested last as it is the base default selector.

Its worth noting that whilst this order is applied, all selectors may not run on a name. This is explained in "How does the rule evaluate a name's format?"

How does the rule evaluate a name's format?

When the format of an identifier is checked, it is checked in the following order:

1. validate leading underscore
2. validate trailing underscore
3. validate prefix
4. validate suffix
5. validate custom
6. validate format

For steps 1-4, if the identifier matches the option, the matching part will be removed. This is done so that you can apply formats like PascalCase without worrying about prefixes or underscores causing it to not match.

One final note is that if the name were to become empty via this trimming process, it is considered to match all formats. An example of where this might be useful is for generic type parameters, where you want all names to be prefixed with T, but also want to allow for the single character T name.

Here are some examples to help illustrate

Name: _IMyInterface Selector:

{
  "leadingUnderscore": "require",
  "prefix": ["I"],
  "format": ["UPPER_CASE", "StrictPascalCase"]
}

1. name = _IMyInterface
2. validate leading underscore
   1. config is provided
   2. check name → pass
   3. Trim underscore → name = IMyInterface
3. validate trailing underscore
   1. config is not provided → skip
4. validate prefix
   1. config is provided
   2. check name → pass
   3. Trim prefix → name = MyInterface
5. validate suffix
   1. config is not provided → skip
6. validate custom
   1. config is not provided → skip
7. validate format
   1. for each format...
      1. format = 'UPPER_CASE'
         1. check format → fail.
            • Important to note that if you supply multiple formats - the name only needs to match one of them!
      2. format = 'StrictPascalCase'
         1. check format → success.
8. success

Name: IMyInterface Selector:

{
  "format": ["StrictPascalCase"],
  "trailingUnderscore": "allow",
  "custom": {
    "regex": "^I[A-Z]",
    "match": false
  }
}

1. name = IMyInterface
2. validate leading underscore
   1. config is not provided → skip
3. validate trailing underscore
   1. config is provided
   2. check name → pass
   3. Trim underscore → name = IMyInterface
4. validate prefix
   1. config is not provided → skip
5. validate suffix
   1. config is not provided → skip
6. validate custom
   1. config is provided
   2. regex = new RegExp("^I[A-Z]")
   3. regex.test(name) === custom.match
   4. fail → report and exit

What happens if I provide a modifiers to a Group Selector?

Some group selectors accept modifiers. For the most part these will work exactly the same as with individual selectors. There is one exception to this in that a modifier might not apply to all individual selectors covered by a group selector.

For example - memberLike includes the enumMember selector, and it allows the protected modifier. An enumMember can never ever be protected, which means that the following config will never match any enumMember:

{
  "selector": "memberLike",
  "modifiers": ["protected"]
}

To help with matching, members that cannot specify an accessibility will always have the public modifier. This means that the following config will always match any enumMember:

{
  "selector": "memberLike",
  "modifiers": ["public"]
}

Examples

Enforce that all variables, functions and properties follow are camelCase

{
  "@typescript-eslint/naming-convention": [
    "error",
    { "selector": "variableLike", "format": ["camelCase"] }
  ]
}

Enforce that private members are prefixed with an underscore

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "memberLike",
      "modifiers": ["private"],
      "format": ["camelCase"],
      "leadingUnderscore": "require"
    }
  ]
}

Enforce that boolean variables are prefixed with an allowed verb

Note: As documented above, the prefix is trimmed before format is validated, thus PascalCase must be used to allow variables such as isEnabled.

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "variable",
      "types": ["boolean"],
      "format": ["PascalCase"],
      "prefix": ["is", "should", "has", "can", "did", "will"]
    }
  ]
}

Enforce that all variables are either in camelCase or UPPER_CASE

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "variable",
      "format": ["camelCase", "UPPER_CASE"]
    }
  ]
}

Enforce that all const variables are in UPPER_CASE

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "variable",
      "modifiers": ["const"],
      "format": ["UPPER_CASE"]
    }
  ]
}

Enforce that type parameters (generics) are prefixed with T

This allows you to emulate the old generic-type-naming rule.

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "typeParameter",
      "format": ["PascalCase"],
      "prefix": ["T"]
    }
  ]
}

Enforce that interface names do not begin with an I

This allows you to emulate the old interface-name-prefix rule.

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "interface",
      "format": ["PascalCase"],
      "custom": {
        "regex": "^I[A-Z]",
        "match": false
      }
    }
  ]
}

Enforce that variable and function names are in camelCase

This allows you to lint multiple type with same pattern.

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": ["variable", "function"],
      "format": ["camelCase"],
      "leadingUnderscore": "allow"
    }
  ]
}

Ignore properties that require quotes

Sometimes you have to use a quoted name that breaks the convention (for example, HTTP headers). If this is a common thing in your codebase, then you have a few options.

If you simply want to allow all property names that require quotes, you can use the requiresQuotes modifier to match any property name that requires quoting, and use format: null to ignore the name.

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": [
        "classProperty",
        "objectLiteralProperty",
        "typeProperty",
        "classMethod",
        "objectLiteralMethod",
        "typeMethod",
        "accessor",
        "enumMember"
      ],
      "format": null,
      "modifiers": ["requiresQuotes"]
    }
  ]
}

If you have a small and known list of exceptions, you can use the filter option to ignore these specific names only:

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "property",
      "format": ["strictCamelCase"],
      "filter": {
        // you can expand this regex to add more allowed names
        "regex": "^(Property-Name-One|Property-Name-Two)$",
        "match": false
      }
    }
  ]
}

You can use the filter option to ignore names with specific characters:

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "property",
      "format": ["strictCamelCase"],
      "filter": {
        // you can expand this regex as you find more cases that require quoting that you want to allow
        "regex": "[- ]",
        "match": false
      }
    }
  ]
}

Note that there is no way to ignore any name that is quoted - only names that are required to be quoted. This is intentional - adding quotes around a name is not an escape hatch for proper naming. If you want an escape hatch for a specific name - you should can use an eslint-disable comment.

Ignore destructured names

Sometimes you might want to allow destructured properties to retain their original name, even if it breaks your naming convention.

You can use the destructured modifier to match these names, and explicitly set format: null to apply no formatting:

{
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "variable",
      "modifiers": ["destructured"],
      "format": null
    }
  ]
}

Enforce the codebase follows ESLint's camelcase conventions

{
  "camelcase": "off",
  "@typescript-eslint/naming-convention": [
    "error",
    {
      "selector": "default",
      "format": ["camelCase"]
    },

    {
      "selector": "variable",
      "format": ["camelCase", "UPPER_CASE"]
    },
    {
      "selector": "parameter",
      "format": ["camelCase"],
      "leadingUnderscore": "allow"
    },

    {
      "selector": "memberLike",
      "modifiers": ["private"],
      "format": ["camelCase"],
      "leadingUnderscore": "require"
    },

    {
      "selector": "typeLike",
      "format": ["PascalCase"]
    }
  ]
}

When Not To Use It

If you do not want to enforce naming conventions for anything.

Resources

• Rule source
• Test source