ESLint Study Portal

Quick recall Q&A

1. When would you create a custom ESLint rule vs using an existing one?

Create custom when:

• Enforcing company-specific conventions
• Preventing known issues specific to your codebase
• Automating repeated code review feedback
• Enforcing architectural boundaries

2. How do you ensure custom rules don't slow down linting?

• Cache AST traversal results
• Use specific node selectors instead of Program:exit where possible
• Avoid complex regex on every node
• Profile with TIMING=1 eslint .

3. How do you test edge cases in custom rules?

• Use RuleTester with valid and invalid cases
• Test boundary conditions (empty files, nested structures)
• Test with TypeScript and JSX syntax
• Test auto-fix output matches expected