🔗 The Great ESLint v9 Migration Adventure: A Developer's Survival Guide

As a frontend developer who has spent years working with complex TypeScript codebases, I’ve learned that solid linting is essential for maintaining long-term code quality. With the release of ESLint v9 and its new flat configuration system, I knew it was time to upgrade — and face the inevitable challenges that come with major version changes.

In this guide, I’ll share my step-by-step experience migrating to ESLint v9 in a TypeScript project — including common roadblocks and how to solve them.

If you’re working with an older ESLint version and a legacy config, this post is for you. Together, we'll break down how to transition to the new flat config system, exploring both its benefits and pitfalls along the way.

➡️ Note: If you're starting a fresh project, I recommend checking out the official ESLint Quick Start Guide instead.

Ready? Let’s dive into the good, the bad, and everything in between when migrating to ESLint v9.