eslint-plugin-square

This plugin contains lint rule definitions and configurations for ESLint specific to Square's needs. It serves mainly to consolidate Square's web frontend linting setup in one place. It is generally not recommended for public usage outside of Square.

Requirements

• ESLint >= 8.18.0
• Node.js ^18.0.0 || >=20.0.0

Usage

Install alongside ESLint via yarn (or npm):

yarn add --dev eslint eslint-plugin-square npm-run-all

If you're creating a new ESLint configuration, refer to ESLint's documentation to determine the correct file format for your project. For example, ESM projects with "type": "module" in their package.json should use an .eslintrc.cjs file format instead of .eslintrc.js.

Once you have an ESLint configuration file, add this plugin to your extends property:

module.exports = {
  extends: ['plugin:square/base'], // Or other configuration.
};

Add the relevant lint scripts in package.json with npm-run-all and include detection for unused disable directives:

{
  "scripts": {
    "lint": "npm-run-all --continue-on-error --aggregate-output --parallel lint:*",
    "lint:js": "eslint --report-unused-disable-directives --cache ."
  }
}

Configure linting to run:

• With the ESLint extension for your IDE
• In your precommit hook (see lint-staged and husky)
• As a build check during CI (in case IDE warnings or the precommit hook are bypassed)

Fix violations using:

• Lint rule autofixers (eslint --fix)
• Lint rule suggestions (a fixer option provided by some rules on highlighted violations in IDEs)
• Codemods (sometimes provided for larger codebase transformations)
• Find-and-replace (with RegExp if necessary)
• Manual fixes

Sometimes, you may not want to fix certain violations, for reasons such as:

• Some code is too risky to change
• A rule may have too many violations and fixing is too tedious / manual
• A rule may have false positives and flag legitimate code
• A rule may not apply in all circumstances (such as a rule that is only useful for test code)
• You may prefer to follow different conventions/styles in your codebase
• You may want to follow-up later to address a specific rule in its own PR

If you prefer not to adopt a specific rule, you can disable it:

• Globally (in the global configuration file)
• In specific directories (in an override in the global configuration file)
• In specific files or on specific lines using comments (// eslint-disable-line no-empty-function)

Configurations

Rules enabled by these configurations should meet the following criteria:

• They make sense in a wide variety of codebases (and have been tested in a variety of Square's applications).
• They are generally acceptable and desirable (in terms of enforcing best practices, consistency, avoiding bugs) to most developers.
• There is a practical migration path (autofixers, codemod, find-and-replace, manual fixes) for enabling them in most applications.

Custom rules

💼 Configurations enabled in.
🔥 Set in the ember configuration.
🔒 Set in the strict configuration.
🔧 Automatically fixable by the --fix CLI option.
💡 Manually fixable by editor suggestions.

Note that we prefer to upstream our custom lint rules to third-party ESLint plugins whenever possible. The rules that still remain here are typically here because:

• We haven't found the appropriate ESLint plugin to upstream them to.
• We haven't found the time to upstream them.
• They are specific to Square in some way / not generic enough.

If you do need to write a custom lint rule here because you can't find an existing lint rule to use or other ESLint plugin to contribute to, be sure to consult astexplorer.net while writing it.

Lint rule ideas often come from:

• A source of frequent "nit" comments in PRs
• Common issues that newcomers stumble on
• Code that indicates a bug, mistake, or bad practice
• Inconsistencies throughout the codebase
• Outdated / obsolete / legacy code

Related

Consider adding other linters not included by plugin:

• check-dependency-version-consistency for monorepos
• commitlint
• ember-template-lint for handlebars files
• eslint-plugin-markdown for markdown code samples
• eslint-plugin-node for Node files
• markdownlint-cli for markdown documentation formatting
• npm-package-json-lint for package.json
• stylelint for CSS files

License

Copyright 2020 Square Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.