new-rule.md

Creating a new rule

Prerequisite

• Ensure ESLint doesn't already have the rule built-in.
• Read the ESLint docs on creating a new rule.
• Look at the commit for how previous rules were added as inspiration. For example, the no-unused-properties rule.

Tip

Use the astexplorer site with the espree parser and ESLint v4 transform to interactively create the initial rule implementation. It lets you inspect the full AST as you would get from ESLint and you can even see the result of your auto-fixer implementation.

Steps

• Run $ npm run create-rule to create files for the new rule.
• Open “test/{RULE_ID}.mjs” and write some tests before implementing the rule.
• Open “rules/{RULE_ID}.js” and implement the rule logic.
• Add the correct meta.type to the rule.
• Open “docs/rules/{RULE_ID}.js” and write some documentation.
• Double check configs/recommended.js and readme.md, make sure the new rule is correctly added.
• Run $ npm test to ensure the tests pass.
• Run $ npm run integration to run the rules against real projects to ensure your rule does not fail on real-world code.
• Open a pull request with a title in exactly the format Add `rule-name` rule, for example, Add `no-unused-properties` rule.
• The pull request description should include the issue it fixes, for example, Fixes #123.
• Run $ npm run run-rules-on-codebase to run the rules against codebase to ensure code in the repository are following your rule, you can ignore this step until your PR is reviewed.