How Turborepo Makes Large JavaScript Projects Fast

Introduction Most projects start with a single repository. Imagine you're building an e-commerce platform: a Next.js storefront for customers, a React Native mobile app, and a NestJS backend API. Splitting these into three repositories feels like the obvious, clean solution. ecommerce-web ecommerce-mobile ecommerce-api For the first few months, this works fine. Then the project grows, and the cracks start to show: You copy utility functions between repositories instead of importing them. You duplicate TypeScript interfaces across the frontend, mobile app, and API. Your frontend and backend drift apart because each repo defines its own version of the same models. Updating one shared component means editing it in three different places. Eventually, maintaining the project becomes harder than building new features. If that sounds familiar, you're not alone — it's exactly the problem monorepos were designed to solve. In this article, we'll cover: What a monorepo actually is, and how it differs from a multi-repo (polyrepo) setup Why engineering teams choose it How Turborepo makes monorepos fast instead of slow A practical, production-ready structure for a Next.js + React Native + NestJS monorepo Common mistakes and best practices Whether you work with React, Next.js, React Native, or NestJS, these concepts will help you build projects that scale without becoming a maintenance burden. The Problem With Multiple Repositories A typical multi-repo setup looks like this: web-app/ mobile-app/ backend-api/ shared-components/ Each repository has its own package.json , dependencies, CI/CD pipeline, Git history, and versioning strategy. It looks clean at first — but as the project grows, several problems appear. 1. Code duplication You write a helper function once: export function formatPrice ( price : number ) { return `$ ${ price . toFixed ( 2 )} ` ; } Both the web app and the mobile app need it, so instead of importing it, someone copies it. Now there are two versions. When one