Eslint 返回 no-unused-vars

Question

I have setup eslint to warn me on unsed vars

rules: {
  '@typescript-eslint/no-unused-vars': ['error', { args: 'none' }],
}

Now I have a typescript class which look like this:

import { User } from './user';

export class MyClass {
  async myMethod(): Promise<User> {
    // Some code
  }
}

When I run eslint I get this error

error  'User' is defined but never used  @typescript-eslint/no-unused-vars

Why is eslint warning me? In my eyes the variable is used.

Answer 1

In your example, we see only the type Promise, which doesn't mean that you are using User in your Method, but only to define a type. Eslint is expected:

import { IUser} from './user'; // interface for User object
import { User } from './user'; // User object

export class MyClass {
  async myMethod(User: string): Promise<IUser> {
    // Some code with User parameter
  }
}

Your Eslint rule will apply only on User object, and not on the interface.

some readings:https://basarat.gitbook.io/typescript/future-javascript/promise

Answer 2

You must disable the base rule as it can report incorrect errors. Reference: @typescript-eslint/no-unused-vars

  "no-unused-vars": "off",
  "@typescript-eslint/no-unused-vars": ["error", { args: "none" }]

User.ts

export class User {
    name: string;
}

MyClass.ts

import { User } from './User'

export class MyClass {
    async myMethod(): Promise<User> {
        // Some code
    }
}

Also this is my bare minimum eslint config

module.exports = {
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint/eslint-plugin"],
  "env": {
    "node": true
  },
  "extends": "eslint:recommended",
  "parserOptions": {
    "ecmaVersion": 6,
    "sourceType": "module"
  },
  "rules": {
    "no-unused-vars": "off",
    "@typescript-eslint/no-unused-vars": ['error'],
  }
}

package.json dependencies

{
  "scripts": {
    "lint": "eslint hello.ts"
  },
  "devDependencies": {
    "@types/eslint": "7.2.4",
    "@types/node": "13.7.7",
    "@typescript-eslint/eslint-plugin": "4.14.1",
    "@typescript-eslint/parser": "4.14.1",
    "eslint": "7.18.0",
    "ts-node": "8.6.2",
    "typescript": "3.8.3"
  }
}