Reinventing Code Writing

Working Code

Start Claude Code in an empty directory and make a request:

> Create a simple REST API server with Express.js.
> A GET /api/health endpoint that returns { status: "ok" }.

Claude generates multiple files like package.json, server.js, etc. Now let's refactor:

> Separate the routes in server.js into a routes/ directory

Claude reorganizes the file structure and updates the import paths automatically.

Try It Yourself

Compare the quality of refactoring requests:

Bad prompt:

> Clean up the code

Good prompt:

> Refactor the error handling middleware in server.js to follow Express best practices.
> Specifically: 1) Extract a custom error class, 2) Separate the error handler middleware, 3) Wrap async/await errors

Compare the two results. The more specific your request, the better the output.

"Why?" — Principles of Prompt Writing

When requesting code from Claude Code, treat it like asking a fellow developer.

The Good Prompt Formula

1. What — what task to perform
2. Where — which file or location
3. How — specific requirements or constraints

> Add a date formatting utility function to src/utils/date.ts.
> Takes an ISO 8601 string and converts it to "March 15, 2025" format.
> Use Intl.DateTimeFormat without libraries like dayjs.

Code Generation vs Refactoring

| Task | Prompt Example | | ----------------- | ------------------------------------------- | | New code | "Create ~" | | Refactoring | "Change ~ to use ~ approach" | | Adding types | "Add TypeScript types to this function" | | Applying patterns | "Convert this code to the Strategy pattern" |

Deep Dive