eslint-plugin-react-hooks-addons

ESLint rule to check unused and potentially unnecessary dependencies in React Hooks.

Why?

eslint-plugin-react-hooks is awesome for linting the dependency array of React Hooks. But it doesn't do one thing: unused dependencies in the useEffect or useLayoutEffect hooks are not reported. Unused variables in useEffect's dependency array are perfectly valid in some use cases. However, they might be unnecessary in some other cases which cause the effect hook to run unintentionally.

Take the following code as an example:

const [user1, setUser1] = useState();
const [user2, setUser2] = useState();

useEffect(() => {
  fetch(`someUrl/${user1}`).then(/* ... */);
  fetch(`someUrl/${user2}`).then(/* ... */);
}, [user1, user2]);

Next day you update the code and remove the second fetch but forget to remove user2 from the dependency array:

const [user1, setUser1] = useState();
const [user2, setUser2] = useState();

useEffect(() => {
  fetch(`someUrl/${user1}`).then(/* ... */);
}, [user1, user2]);

Then the useEffect will run whenever user1 or user2 changes, which is probably not your intention. Similar errors occur more frequently when the hook callback function is large and there is a long dependency array. This eslint plugin checks and reports this kind of error.

What if I have a value which is not used in the hook function scope but I want the effect hook to run whenever that value has changed? You could prepend a /* effect dep */ comment to the value in dependency array then it will be skipped during linting. It brings an addition benefit: the value is explicitly marked as effectful so that other people coming across the code will understand it's not a programmatic error.

useEffect(() => {
  fetch(`someUrl/${user1}`).then(/* ... */);
- }, [user1, user2]);
+ }, [user1, /* effect dep */ user2]);

Install

with npm

npm install -D eslint-plugin-react-hooks-addons

or with Yarn

yarn add -D eslint-plugin-react-hooks-addons

Usage

Flat config

import reactHooksAddons from 'eslint-plugin-react-hooks-addons';

export default [
  reactHooksAddons.configs.recommended
  // other configs...
];

Or, use a custom configuration:

import reactHooksAddons from 'eslint-plugin-react-hooks-addons';

export default [
  // other configs...
  {
    plugins: {
      'react-hooks-addons': reactHooksAddons
    },
    rules: {
      'react-hooks-addons/no-unused-deps': 'warn'
    }
  }
];

Legacy config

{
  "extends": ["plugin:react-hooks-addons/recommended-legacy"]
}

Or, use a custom configuration:

{
  "plugins": ["react-hooks-addons"],
  "rules": {
    "react-hooks-addons/no-unused-deps": "warn"
  }
}

Effect deps

Explicitly mark a dependency as effectful with /* effect dep */ comment:

useEffect(() => {
  // ...
}, [unusedVar, /* effect dep */ effectVar]);

Then only the unusedVar will be reported as an unused dependency.

Options

effectComment

You can use a different comment to mark dependencies as effectful:

"rules": {
  "react-hooks-addons/no-unused-deps": [
    "warn",
    {
      "effectComment": "effectful"
    }
  ]
}

additionalHooks

The rule checks useEffect and useLayoutEffect hooks by default. It can be configured to check dependencies of custom hooks with the additionalHooks option. This option accepts a pattern key which is a regex pattern. If you set the replace key to true, it would replace the default hooks.

"rules": {
  "react-hooks-addons/no-unused-deps": [
    "warn",
    {
      "additionalHooks": {
        "pattern": "useMyCustomHook|useMyOtherCustomHook",
        "replace": true
      }
    }
  ]
}

Note: this eslint plugin is supposed to work in tandem with eslint-plugin-react-hooks, as it doesn't check things that have already been reported by that plugin.

License

MIT Licensed.