TypeScript Project References for Monorepo Builds

In a monorepo, building one package rebuilds all its dependencies from scratch. Type checking is slow and packages cannot reference each other's type information without full recompilation.

Use TypeScript Project References to enable incremental cross-package compilation.

// packages/core/tsconfig.json
{
  "compilerOptions": {
    "composite": true,
    "declaration": true,
    "declarationMap": true,
    "outDir": "./dist"
  }
}

// packages/app/tsconfig.json
{
  "compilerOptions": { "outDir": "./dist" },
  "references": [
    { "path": "../core" }
  ]
}

// Root tsconfig.json
{
  "references": [
    { "path": "packages/core" },
    { "path": "packages/app" }
  ],
  "files": []
}

# Build all with dependency order
tsc --build
# Build only changed packages
tsc --build --incremental

Project references allow tsc to cache .d.ts outputs of referenced projects. When only one package changes, tsc rebuilds only that package and its dependents, not the entire tree.