eslint vs prettier vs standard vs xo vs semistandard
JavaScriptコードの品質保証とフォーマット戦略
eslintprettierstandardxosemistandard類似パッケージ:
JavaScriptコードの品質保証とフォーマット戦略

eslintprettiersemistandardstandardxoはすべてJavaScriptプロジェクトにおけるコード品質と一貫性を確保するためのツールですが、それぞれアプローチが異なります。eslintは高度にカスタマイズ可能な静的解析ツールで、潜在的なバグやスタイル違反を検出します。prettierは「意見の強い」コードフォーマッタで、構文を再構成して一貫した見た目を強制します。一方、standardsemistandardxoはルールセットとしてeslintをラップし、設定不要の体験を提供します。semistandardstandardの派生でセミコロンを許容し、xoは現代的なESLintプリセットとしてTypeScriptやモダン構文への対応を重視しています。

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eslint70,587,00026,6872.99 MB1061ヶ月前MIT
prettier64,737,69151,2798.58 MB1,4677日前MIT
standard573,13829,397164 kB1291年前MIT
xo239,8737,93784.6 kB612ヶ月前MIT
semistandard25,1381,41747.6 kB03年前MIT

JavaScriptコード品質ツール徹底比較:ESLint vs Prettier vs Standard系

フロントエンド開発において、コードの一貫性と品質を保つことはチーム生産性の根幹です。eslintprettiersemistandardstandardxoはこの課題に異なる角度からアプローチします。それぞれの本質的な違いを、実際のコード例を交えて解説します。

🧩 基本コンセプト:静的解析 vs フォーマット vs 設定済みルールセット

eslint は静的解析エンジンそのものです。ルールを個別に有効化・無効化でき、カスタムルールの作成も可能です。

// .eslintrc.js
module.exports = {
  rules: {
    'no-console': 'warn',
    'prefer-const': 'error'
  }
};

prettier はコードの「見た目」だけを扱います。構文をパースして再出力することで、フォーマットの不一致を根本から排除します。

// prettier.config.js
module.exports = {
  semi: false,
  singleQuote: true
};

standard / semistandard / xoeslintの上に構築された「意見のある」プリセットです。設定ファイル不要が売りですが、内部的にはESLintルールを適用しています。

# standardの実行例(設定ファイル不要)
npx standard

⚙️ 設定の柔軟性:自由度 vs 制約

ESLint:完全カスタマイズ可能

ESLintはルールごとの設定が可能です。たとえば、no-unused-varsを警告レベルにしたり、特定の変数名を除外できます。

// .eslintrc.js
module.exports = {
  rules: {
    'no-unused-vars': ['warn', { varsIgnorePattern: '^_' }]
  }
};

Prettier:見た目だけを制御

Prettierの設定項目は限られています(インデント幅、セミコロンの有無など)。ロジックに関わるルール(未使用変数など)は一切扱いません。

// prettier.config.js
module.exports = {
  tabWidth: 2,
  printWidth: 80
};

Standard系:固定ルールセット

standardはセミコロン禁止、semistandardはセミコロン許容という違い以外、ほぼ同一のルールを持ちます。xoはこれらより若干柔軟で、.xo-config.jsで一部ルールを上書きできます。

// .xo-config.js (xoの場合)
module.exports = {
  rules: {
    'no-console': 'off'
  }
};

💡 注:standardsemistandardは設定ファイルによるカスタマイズを公式にサポートしていません。xoのみが限定的な上書きを許容します。

🔌 統合方法:単体利用 vs 組み合わせ

ESLint + Prettierの黄金コンビ

多くのプロジェクトでは、ESLint(ロジックチェック)とPrettier(フォーマット)を併用します。競合を避けるため、ESLint側でフォーマット関連ルールを無効化します。

// .eslintrc.js
module.exports = {
  extends: [
    'eslint:recommended',
    'prettier' // eslint-config-prettierでフォーマットルールを無効化
  ],
  plugins: ['prettier'],
  rules: {
    'prettier/prettier': 'error' // Prettierの違反をESLintエラーとして報告
  }
};

Standard系:単体で完結

standard系は単体で実行可能です。内部でESLintとPrettier相当の処理を統合していますが、詳細な制御はできません。

# standardの実行
npx standard --fix

# xoの実行
npx xo --fix

🧪 実際のコード変換例

同じソースコードを各ツールで処理した結果を比較します。

元のコード:

function hello( name ){
  console.log('Hello, ' + name);
  return name;
}

ESLint(推奨ルール + fix)

// .eslintrc.jsに基本ルールを設定
function hello(name) {
  console.log('Hello, ' + name);
  return name;
}
// → 引数のスペースを修正('space-in-parens'ルール)

Prettier

function hello(name) {
  console.log('Hello, ' + name)
  return name
}
// → セミコロン削除、インデント統一(デフォルト設定)

Standard

function hello (name) {
  console.log('Hello, ' + name)
  return name
}
// → 関数名後のスペースを追加(Standard独自ルール)

Semistandard

function hello (name) {
  console.log('Hello, ' + name);
  return name;
}
// → Standardと同じだがセミコロンを保持

XO

function hello(name) {
  console.log('Hello, ' + name)
  return name
}
// → Prettierに近いが、関数引数のスペースは削除(XOのデフォルト)

🛠️ プロジェクトへの導入戦略

大規模チーム or 複雑な要件 → ESLint + Prettier

  • 利点:細かいルール調整が可能、フレームワーク固有ルール(React Hooksなど)に対応
  • 注意点:初期設定に時間がかかる、.eslintrcのメンテナンスが必要

小規模チーム or スタートアップ → XO

  • 利点:最新JS/TS対応、設定不要で高品質、一部カスタマイズ可
  • 注意点:依存関係がやや多い

教育目的 or 超シンプル志向 → Standard/Semistandard

  • 利点:ゼロ設定で即実行、学習コストが低い
  • 注意点:カスタマイズ不能、特殊なニーズには対応できない

📊 機能比較表

機能eslintprettierstandardsemistandardxo
静的解析✅ 完全対応✅ (内部でESLint)✅ (内部でESLint)✅ (内部でESLint)
コードフォーマット△ ルール依存✅ 専門
設定不要△ 必要に応じて△ デフォルトあり
カスタマイズ性✅ 完全自由△ 見た目のみ△ 限定的
TypeScript対応✅ プラグインで✅ デフォルトで
セミコロン許容△ ルール次第△ 設定次第△ 設定可能

💡 最終アドバイス

  • 「フォーマットは機械に任せて、人間はロジックに集中すべき」 という思想なら、prettierは必須です。
  • 「プロジェクト独自の規約を厳密に守りたい」 なら、eslintを直接使うのが確実です。
  • 「設定に時間をかけず、すぐに品質を確保したい」 なら、xoが最もバランスが取れています。
  • standard/semistandard は、本当にシンプルなプロジェクトか、教育用途以外では選択肢から外しても良いでしょう。

重要なのは、ツールの選択ではなく「チーム内で合意されたルールを自動化すること」です。どのツールを選ぶにせよ、CIで強制チェックを入れることを忘れないでください。

選び方: eslint vs prettier vs standard vs xo vs semistandard
  • eslint:

    eslintは、プロジェクト固有のコーディング規約や複雑な静的解析ルールが必要な場合に最適です。大規模チームや長期保守プロジェクトでは、細かいルール調整が不可欠であり、プラグインによる拡張性(React、TypeScriptなど)も活かせます。ただし、初期設定とメンテナンスコストがかかるため、小さなプロジェクトにはオーバーキルになる可能性があります。

  • prettier:

    prettierは、コードの見た目(インデント、改行、クォートなど)に関する議論を完全に排除したい場合に選ぶべきです。開発者がフォーマットに意識を割く必要がなくなり、PRのレビューがロジックに集中できます。ただし、eslintと併用する際はルールの競合を避けるためeslint-config-prettierの導入が必須です。

  • standard:

    standardは、設定ファイルなしで即座に使える厳格なスタイルガイドを求めている場合に適しています。初心者チームや小規模プロジェクトで、迅速にコード品質を確保したい場面で有効です。しかし、ルールの変更がほぼ不可能であるため、プロジェクトの成長とともに制約を感じる可能性があります。

  • xo:

    xoは、最新のJavaScript/TypeScript機能を積極的に採用するモダンプロジェクト向けです。ESLintのベストプラクティスを組み込みつつ、合理的なデフォルト設定を提供します。設定のオーバーライドも可能で、standardより柔軟性があります。ただし、依存関係がやや多めで、軽量さを求めるプロジェクトには向かないかもしれません。

  • semistandard:

    semistandardは、standardの哲学(設定不要・シンプル)を維持しつつ、セミコロンの使用を許容したいチーム向けです。既存コードベースにセミコロンが混在している場合や、チーム内でセミコロンの有無について合意が取れない場合に妥協案として機能します。ただし、standardと同様にカスタマイズ性が低く、特殊なニーズには対応できません。

eslint のREADME

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ESLint

Website | Configure ESLint | Rules | Contribute to ESLint | Report Bugs | Code of Conduct | X | Discord | Mastodon | Bluesky

ESLint is a tool for identifying and reporting on patterns found in ECMAScript/JavaScript code. In many ways, it is similar to JSLint and JSHint with a few exceptions:

  • ESLint uses Espree for JavaScript parsing.
  • ESLint uses an AST to evaluate patterns in code.
  • ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.

Table of Contents

  1. Installation and Usage
  2. Configuration
  3. Version Support
  4. Code of Conduct
  5. Filing Issues
  6. Frequently Asked Questions
  7. Releases
  8. Security Policy
  9. Semantic Versioning Policy
  10. License
  11. Team
  12. Sponsors
  13. Technology Sponsors

Installation and Usage

Prerequisites: Node.js (^18.18.0, ^20.9.0, or >=21.1.0) built with SSL support. (If you are using an official Node.js distribution, SSL is always built in.)

You can install and configure ESLint using this command:

npm init @eslint/config@latest

After that, you can run ESLint on any file or directory like this:

npx eslint yourfile.js

pnpm Installation

To use ESLint with pnpm, we recommend setting up a .npmrc file with at least the following settings:

auto-install-peers=true
node-linker=hoisted

This ensures that pnpm installs dependencies in a way that is more compatible with npm and is less likely to produce errors.

Configuration

You can configure rules in your eslint.config.js files as in this example:

import { defineConfig } from "eslint/config";

export default defineConfig([
	{
		files: ["**/*.js", "**/*.cjs", "**/*.mjs"],
		rules: {
			"prefer-const": "warn",
			"no-constant-binary-expression": "error",
		},
	},
]);

The names "prefer-const" and "no-constant-binary-expression" are the names of rules in ESLint. The first value is the error level of the rule and can be one of these values:

  • "off" or 0 - turn the rule off
  • "warn" or 1 - turn the rule on as a warning (doesn't affect exit code)
  • "error" or 2 - turn the rule on as an error (exit code will be 1)

The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the configuration docs).

Version Support

The ESLint team provides ongoing support for the current version and six months of limited support for the previous version. Limited support includes critical bug fixes, security issues, and compatibility issues only.

ESLint offers commercial support for both current and previous versions through our partners, Tidelift and HeroDevs.

See Version Support for more details.

Code of Conduct

ESLint adheres to the OpenJS Foundation Code of Conduct.

Filing Issues

Before filing an issue, please be sure to read the guidelines for what you're reporting:

Frequently Asked Questions

Does ESLint support JSX?

Yes, ESLint natively supports parsing JSX syntax (this must be enabled in configuration). Please note that supporting JSX syntax is not the same as supporting React. React applies specific semantics to JSX syntax that ESLint doesn't recognize. We recommend using eslint-plugin-react if you are using React and want React semantics.

Does Prettier replace ESLint?

No, ESLint and Prettier have different jobs: ESLint is a linter (looking for problematic patterns) and Prettier is a code formatter. Using both tools is common, refer to Prettier's documentation to learn how to configure them to work well with each other.

What ECMAScript versions does ESLint support?

ESLint has full support for ECMAScript 3, 5, and every year from 2015 up until the most recent stage 4 specification (the default). You can set your desired ECMAScript syntax and other settings (like global variables) through configuration.

What about experimental features?

ESLint's parser only officially supports the latest final ECMAScript standard. We will make changes to core rules in order to avoid crashes on stage 3 ECMAScript syntax proposals (as long as they are implemented using the correct experimental ESTree syntax). We may make changes to core rules to better work with language extensions (such as JSX, Flow, and TypeScript) on a case-by-case basis.

In other cases (including if rules need to warn on more or fewer cases due to new syntax, rather than just not crashing), we recommend you use other parsers and/or rule plugins. If you are using Babel, you can use @babel/eslint-parser and @babel/eslint-plugin to use any option available in Babel.

Once a language feature has been adopted into the ECMAScript standard (stage 4 according to the TC39 process), we will accept issues and pull requests related to the new feature, subject to our contributing guidelines. Until then, please use the appropriate parser and plugin(s) for your experimental feature.

Which Node.js versions does ESLint support?

ESLint updates the supported Node.js versions with each major release of ESLint. At that time, ESLint's supported Node.js versions are updated to be:

  1. The most recent maintenance release of Node.js
  2. The lowest minor version of the Node.js LTS release that includes the features the ESLint team wants to use.
  3. The Node.js Current release

ESLint is also expected to work with Node.js versions released after the Node.js Current release.

Refer to the Quick Start Guide for the officially supported Node.js versions for a given ESLint release.

Where to ask for help?

Open a discussion or stop by our Discord server.

Why doesn't ESLint lock dependency versions?

Lock files like package-lock.json are helpful for deployed applications. They ensure that dependencies are consistent between environments and across deployments.

Packages like eslint that get published to the npm registry do not include lock files. npm install eslint as a user will respect version constraints in ESLint's package.json. ESLint and its dependencies will be included in the user's lock file if one exists, but ESLint's own lock file would not be used.

We intentionally don't lock dependency versions so that we have the latest compatible dependency versions in development and CI that our users get when installing ESLint in a project.

The Twilio blog has a deeper dive to learn more.

Releases

We have scheduled releases every two weeks on Friday or Saturday. You can follow a release issue for updates about the scheduling of any particular release.

Security Policy

ESLint takes security seriously. We work hard to ensure that ESLint is safe for everyone and that security issues are addressed quickly and responsibly. Read the full security policy.

Semantic Versioning Policy

ESLint follows semantic versioning. However, due to the nature of ESLint as a code quality tool, it's not always clear when a minor or major version bump occurs. To help clarify this for everyone, we've defined the following semantic versioning policy for ESLint:

  • Patch release (intended to not break your lint build)
    • A bug fix in a rule that results in ESLint reporting fewer linting errors.
    • A bug fix to the CLI or core (including formatters).
    • Improvements to documentation.
    • Non-user-facing changes such as refactoring code, adding, deleting, or modifying tests, and increasing test coverage.
    • Re-releasing after a failed release (i.e., publishing a release that doesn't work for anyone).
  • Minor release (might break your lint build)
    • A bug fix in a rule that results in ESLint reporting more linting errors.
    • A new rule is created.
    • A new option to an existing rule that does not result in ESLint reporting more linting errors by default.
    • A new addition to an existing rule to support a newly-added language feature (within the last 12 months) that will result in ESLint reporting more linting errors by default.
    • An existing rule is deprecated.
    • A new CLI capability is created.
    • New capabilities to the public API are added (new classes, new methods, new arguments to existing methods, etc.).
    • A new formatter is created.
    • eslint:recommended is updated and will result in strictly fewer linting errors (e.g., rule removals).
  • Major release (likely to break your lint build)
    • eslint:recommended is updated and may result in new linting errors (e.g., rule additions, most rule option updates).
    • A new option to an existing rule that results in ESLint reporting more linting errors by default.
    • An existing formatter is removed.
    • Part of the public API is removed or changed in an incompatible way. The public API includes:
      • Rule schemas
      • Configuration schema
      • Command-line options
      • Node.js API
      • Rule, formatter, parser, plugin APIs

According to our policy, any minor update may report more linting errors than the previous release (ex: from a bug fix). As such, we recommend using the tilde (~) in package.json e.g. "eslint": "~3.1.0" to guarantee the results of your builds.

License

MIT License

Copyright OpenJS Foundation and other contributors, <www.openjsf.org>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Team

These folks keep the project moving and are resources for help.

Technical Steering Committee (TSC)

The people who manage releases, review feature requests, and meet regularly to ensure ESLint is properly maintained.

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Nicholas C. Zakas
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Francesco Trotta
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Milos Djermanovic

Reviewers

The people who review and implement new features.

唯然's Avatar
唯然
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Nitin Kumar

Committers

The people who review and fix bugs and help triage issues.

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fnx
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Josh Goldberg ✨
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Sweta Tanwar
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Tanuj Kanti
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루밀LuMir
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Pixel998

Website Team

Team members who focus specifically on eslint.org

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Amaresh S M
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Harish
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Percy Ma

Sponsors

The following companies, organizations, and individuals support ESLint's ongoing maintenance and development. Become a Sponsor to get your logo on our READMEs and website.

Platinum Sponsors

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Gold Sponsors

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Bronze Sponsors

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Technology Sponsors

Technology sponsors allow us to use their products and services for free as part of a contribution to the open source ecosystem and our work.

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