ESLint with React gives `no-unused-vars` errors

104
votes

I've setup eslint & eslint-plugin-react.

When I run ESLint, the linter returns no-unused-vars errors for each React component.

I'm assuming it's not recognizing that I'm using JSX or React syntax. Any ideas?

Example:

app.js

import React, { Component } from 'react';
import Header from './header.js';

export default class App extends Component {
  render() {
    return (
      <div>
        <Header />
        {this.props.children}
      </div>
    );
  }
}

Linter Errors:

/my_project/src/components/app.js
  1:8  error  'React' is defined but never used   no-unused-vars
  2:8  error  'Header' is defined but never used  no-unused-vars

Here is my .eslintrc.json file:

{
    "env": {
        "browser": true,
        "es6": true
    },
    "extends": "eslint:recommended",
    "parserOptions": {
        "ecmaFeatures": {
            "experimentalObjectRestSpread": true,
            "jsx": true
        },
        "sourceType": "module"
    },
    "plugins": [
        "react"
    ],
    "rules": {
        "react/jsx-filename-extension": [1, { "extensions": [".js", ".jsx"] }],
        "indent": [
            "error",
            2
        ],
        "linebreak-style": [
            "error",
            "unix"
        ],
        "quotes": [
            "error",
            "single"
        ],
        "semi": [
            "error",
            "always"
        ]
    }
}
9
javascriptreactjsjsxeslint
You're importing React while not using it, you're just using Component, which is correctly imported. – GMaiolo
That makes sense - but why would Header also have the error? (You actually need to import React, otherwise when the JSX gets transpiled, it will give an error) – Don P
This shouldn't be happening by now. What's your eslint version? github.com/eslint/eslint/issues/1905 – daniloprates

9 Answers

210
votes

First, install the following module npm install --save-dev eslint-plugin-react.

Then, in your .eslintrc.json, under extends, include the following plugin:

'extends': [
    'plugin:react/recommended'
]

Source

62
votes

To solve this only problem without adding new rules from react/recommended install eslint-plugin-react:

npm install eslint-plugin-react --save-dev

add in .eslintrc.js:

"plugins": ["react"]

and:

"rules": {   
     "react/jsx-uses-react": "error",   
     "react/jsx-uses-vars": "error" 
}
15
votes

Since I found this while googling, you should know that this simple rule is enough to prevent this message:

react/jsx-uses-react

The react/recommended set of rules adds many other rules you may not want.

9
votes

In my case I needed to add in your .eslintrc.js:

'extends': [
    'plugin:react/recommended'
]

plus a specific tweaking to rid of preact import: import { h } from 'preact' but you can use this example to get rid of your specific warnings like so:

    "no-unused-vars": [
        "error",
        {
            "varsIgnorePattern": "^h$"
        }
    ],
7
votes

Quickest fix

To ignore all TitleCase variables, add this to your ESLint config:

{
    "rules": {
        "no-unused-vars": [
            "error",
            {
                "varsIgnorePattern": "^[A-Z]"
            }
        ]
    ]
}

Correct fix

Use eslint-plugin-react to ignore React variables. 

npm install eslint-plugin-react -D

Add this to your ESLint config:

{
    "plugins": [
        "react"
    ],
    "rules": {
        "react/jsx-uses-vars": "error",
        "react/jsx-uses-react": "error"
    }
}

Suggested fix

Use eslint-plugin-react to improve your JSX usage, not just to silence this error.

npm install eslint-plugin-react -D

Add this to your ESLint config:

{
    "extends": [
        "plugin:react/recommended"
    ]
}

If you use XO, refer to eslint-config-xo-react.

1
votes

I have the same error as well as I started to learn React yesterday. The terminal show the error and it is pretty straightforward to ignore the unused variable error.

Error from the terminal:

Line 5:17:  'setBlog' is assigned a value but never used  no-unused-vars
Search for the keywords to learn more about each warning.

Just add // eslint-disable-next-line this line before the variable which you have the error of unused variable. Like,

// eslint-disable-next-line
const [blogs, setBlog] = useState(... my code)
1
votes

According to Official Docs of Eslint have you tried this

/* eslint no-unused-vars : "off" */

add this line as it is inside anywhere in your code. Hopefully you warning may go away and it may help you

-1
votes

If you create the project throught create-react-app CLI,You can npm run eject,and edit the package.json "eslintConfig" field,like this:

`"eslintConfig": {
    "extends": "react-app",
    "rules": {
      "eqeqeq": "off",
      "no-unused-vars": "off",
    }
  },`

the eslint will be closed

-1
votes

if you are using Create-react-app, there is no need to install anything or Eject, the simple solution is:

since the no-unused-vars-errors is thrown from webpackHotDevClient.js, you just need to go to /node_modules/react-scripts/config/webpack.config.dev.js. on "new ESLintPlugin" rules just add :

'react/jsx-uses-react': 'error',
'react/jsx-uses-vars': 'error',
'no-unused-vars': 0