eslint-plugin-redundant-undefined

Forbids optional parameters to include an explicit undefined in their type and requires to use undefined in optional properties.

Installation

$ npm i eslint-plugin-redundant-undefined @typescript-eslint/parser --save-dev

Usage

Add redundant-undefined to the plugins section of your .eslintrc configuration file. You can omit the eslint-plugin- prefix:

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["redundant-undefined"]
}

Then configure the rules you want to use under the rules section.

{
  "rules": {
    "redundant-undefined/redundant-undefined": "error"
  }
}

Rule Details

• Avoid explicitly specifying undefined as a type for a parameter/property which is already optional

Options

• followExactOptionalPropertyTypes - Requires explicitly specifying undefined as a type for a parameter which is already optional., this provides the correct semantics for people who have exactOptionalPropertyType: true

Examples

Examples of incorrect code:

function f(s?: undefined | string): void {}

function f(s?: number | undefined | string): void {}

interface I {
  a?: string | undefined;
}

class C {
  a?: string | undedined;
}

Examples of correct code:

function f(s?: string): void {}

interface I {
  a?: string;
}

interface I {
  a?: any;
}

class C {
  a?: string;
}

Examples of incorrect code for the { "followExactOptionalPropertyTypes": true }:

interface I {
  p?: string;
}

class C {
  private p?: number;
}

abstract class C {
  abstract p?: string;
}

Examples of correct code for the { "followExactOptionalPropertyTypes": true }:

interface I {
  p?: string | undefined;
}

interface I {
  p?: any;
}

class C {
  private p?: number | undefined;
}

abstract class C {
  abstract p?: string | undefined;
}

License and Copyright

This software is released under the terms of the MIT license.