Project Overview

Typestep is a CLI tool designed to help teams progressively adopt TypeScript in existing JavaScript projects. When migrating large codebases, running tsc for the first time can reveal hundreds of type errors—far too many to fix at once without disrupting development.

Typestep solves this problem by enabling an incremental migration strategy:

1. Prevent regression - Ensure new code follows TypeScript rules
2. Catalog existing errors - Creates a config file that tracks all current type issues
3. Enforce immediately - Lets you add TypeScript checking to CI without breaking builds

Configuration Flexibility

Typestep offers powerful configuration options through its typestep.config.ts file:

import type { TypestepConfig } from 'typestep'

export default {
  ignoredFiles: {
    // Ignore all errors in this file
    'src/legacy-api-client.ts': true,
    'src/components/UserDashboard.tsx': {
      // Ignore only specific error codes in this file
      ignoredTsErrorCodes: ['TS2339', 'TS2345']
    },
    // Use functions for dynamic filtering
    'src/utils/date-formatter.ts': ({ error }) => {
      return error.includes('Property does not exist')
    }
  },
  // Global error codes to ignore in all files
  ignoredTsErrorCodes: ['TS2322'],
} satisfies TypestepConfig

This approach gives you precise control over your migration strategy while keeping your CI pipeline running smoothly.

Learn More

For a detailed walkthrough showing how to use Typestep in a real project, including code examples and step-by-step migration strategy, read my blog post:

Introducing Typestep: TypeScript Migration, One Step at a Time