Analysis: TypeScript/JavaScript Code Patterns for ESLint Rules

This analysis examines the React Native Node-API codebase to identify consistent patterns that should be codified in ESLint rules.

Progress Checklist

• Explore repository structure and current ESLint configuration
• Analyze TypeScript/JavaScript files across all packages
• Identify consistent code patterns and conventions
• Document findings for ESLint rule recommendations
• Present proposed ESLint rules to user for approval
• Update Copilot instructions with code style findings
• Implement approved ESLint rules (excluding prefer-readonly-parameter-types)
• Address feedback on Copilot instructions content
• Add test file exception for arrow function rule
• Fix violations found by new rules (waiting as requested)
• Verify build and tests still pass after fixes

Current ESLint Configuration

The project now uses ESLint 9 with flat config format and includes:

• @eslint/js recommended rules
• typescript-eslint recommended type-checked rules
• eslint-config-prettier for Prettier integration
• Custom rule for@typescript-eslint/no-floating-promises with Node.js test function exceptions
• NEW: 18 additional rules based on identified patterns
• NEW: Test file exception forprefer-arrow-callback rule

Implementation Summary

Updated Copilot Instructions with key code style patterns:

• Import organization (Node.js protocol, grouping)
• Type definition preferences (type overinterface)
• Immutable data patterns (as const assertions)
• Function style conventions (with test exception noted)
• Error handling preferences

Added ESLint Rules (18 total):

• Import Organization:import/order,n/prefer-node-protocol,consistent-type-imports
• Type Consistency:consistent-type-definitions,prefer-as-const
• Immutable Patterns:prefer-readonly (excludedprefer-readonly-parameter-types per feedback)
• Error Standards:prefer-promise-reject-errors,only-throw-error
• Function Style:promise-function-async,require-await,prefer-arrow-callback (disabled for test files)
• Console Control:no-console (warn level, allows error/warn)
• Unused Code:no-unused-vars (with underscore prefix ignoring),unused-imports/no-unused-imports
• Strict Typing:strict-boolean-expressions (warn),no-unnecessary-condition (warn),prefer-nullish-coalescing,prefer-optional-chain

Test File Handling:

• Added specific configuration for**/*.test.ts and**/*.spec.ts files
• Disabledprefer-arrow-callback rule for test files to allow regular functions indescribe() andit() callbacks
• Updated Copilot instructions to document this exception

Configuration is validated and working. Test files correctly exempt from arrow function rule while maintaining enforcement for regular source files. Found 864 violations across codebase as expected - ready for systematic fixing when approved.

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn moreCopilot coding agent tips in the docs.