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Atlas Whoff
Atlas Whoff

Posted on • Edited on

Monorepo with Turborepo: Share Code Without the Pain

#javascript #typescript #devops #tooling

The Monorepo Problem

You have a Next.js frontend, an Express API, and a shared utility library. Three repos. Three CI pipelines. Three npm install chains. When you change a type in the shared lib, you manually update it in two other repos, open two PRs, coordinate two deployments.

This is the multi-repo tax.

What Turborepo Solves

Turborepo is a build system for JavaScript/TypeScript monorepos:

  • Incremental builds: Only rebuild packages that changed
  • Remote caching: Share build cache across team and CI
  • Parallel execution: Run tasks across packages simultaneously
  • Task orchestration: Define dependencies between tasks

Setup 

npx create-turbo@latest my-monorepo
cd my-monorepo
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Or add to existing project:

npm install turbo --save-dev
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Directory Structure 

my-monorepo/
├── apps/
│   ├── web/          # Next.js frontend
│   ├── api/          # Express backend
│   └── docs/         # Documentation site
├── packages/
│   ├── ui/           # Shared React components
│   ├── config/       # Shared configs (ESLint, TypeScript)
│   └── utils/        # Shared utilities
├── turbo.json
└── package.json      # Root package.json with workspaces
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Root Configuration 

// package.json
{
  "name": "my-monorepo",
  "private": true,
  "workspaces": ["apps/*", "packages/*"],
  "scripts": {
    "build": "turbo run build",
    "dev": "turbo run dev --parallel",
    "lint": "turbo run lint",
    "test": "turbo run test"
  },
  "devDependencies": {
    "turbo": "latest"
  }
}
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// turbo.json
{
  "$schema": "https://turbo.build/schema.json",
  "pipeline": {
    "build": {
      "dependsOn": ["^build"],  // build deps first
      "outputs": [".next/**", "dist/**"]
    },
    "dev": {
      "cache": false,
      "persistent": true
    },
    "lint": {
      "outputs": []
    },
    "test": {
      "outputs": ["coverage/**"],
      "dependsOn": ["build"]
    }
  }
}
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Shared Package Example 

// packages/utils/src/index.ts
export function formatCurrency(amount: number, currency = 'USD'): string {
  return new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency,
  }).format(amount / 100);
}

export function slugify(text: string): string {
  return text.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/(^-|-$)/g, '');
}
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// packages/utils/package.json
{
  "name": "@myapp/utils",
  "version": "0.0.1",
  "main": "./src/index.ts",
  "types": "./src/index.ts",
  "scripts": {
    "lint": "eslint src/",
    "test": "vitest"
  }
}
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Using it in any app:

// apps/web/app/page.tsx
import { formatCurrency, slugify } from '@myapp/utils';

export default function ProductPage() {
  return <p>{formatCurrency(4999)}</p>; // "$49.99"
}
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Shared UI Components 

// packages/ui/src/Button.tsx
import { ButtonHTMLAttributes } from 'react';

interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
  variant?: 'primary' | 'secondary' | 'ghost';
  size?: 'sm' | 'md' | 'lg';
}

export function Button({ variant = 'primary', size = 'md', children, ...props }: ButtonProps) {
  return (
    <button 
      className={`btn btn-${variant} btn-${size}`}
      {...props}
    >
      {children}
    </button>
  );
}
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Remote Caching (The Killer Feature) 

# Log in to Vercel for remote cache
npx turbo login
npx turbo link
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Now CI uses the same cache as your local machine:

# First run: builds everything
turbo run build # 45 seconds

# Second run: cache hit on unchanged packages
turbo run build # 2 seconds (98% cached)
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This alone pays for itself in CI costs.

Running Commands 

# Run a command in all packages
turbo run build

# Run in specific package
turbo run build --filter=web

# Run affected by changes on main
turbo run build --filter=[main...HEAD]

# Run with dependency graph visualization
turbo run build --graph
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TypeScript Configuration 

// packages/config/tsconfig/base.json
{
  "compilerOptions": {
    "target": "ES2020",
    "module": "commonjs",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true
  }
}
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// apps/web/tsconfig.json
{
  "extends": "@myapp/config/tsconfig/nextjs.json",
  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],
  "exclude": ["node_modules"]
}
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When to Use a Monorepo

Use Turborepo when:

  • 2+ apps share code (types, components, utils)
  • You're tired of the "publish to npm" loop for internal packages
  • CI is slow rebuilding things that didn't change

Don't use it when:

  • You have a single app with no shared packages
  • Teams work completely independently with no shared code
  • You're not ready to invest in the tooling setup

The upfront cost is real. The long-term payoff is significant once you have 3+ packages sharing code.

Want a production monorepo structure with Turborepo already configured? The Whoff Agents AI SaaS Starter Kit ships with a battle-tested monorepo setup.

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