Compiler API & References

Preview — 3 of 10 questions

What does verbatimModuleSyntax enforce?

javascript

// tsconfig: "verbatimModuleSyntax": true

// File: index.ts
import { User } from './types';  // User is a type-only export
import { fetchUser } from './api'; // fetchUser is a function

export { User }; // (A)?
export { fetchUser }; // (B)?

ABoth error — all exports must use export type

BBoth work — TypeScript determines which to erase automatically

C(A) errors — type-only imports must use import type and export type; (B) is fine

D(B) errors — only type exports are allowed with verbatimModuleSyntax

What is the purpose of project references?

javascript

// apps/web/tsconfig.json
{
  "compilerOptions": { "composite": true, "outDir": "./dist" },
  "references": [
    { "path": "../../packages/types" },
    { "path": "../../packages/ui" }
  ]
}

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

AReferences are just documentation — TypeScript ignores them for compilation

Bcomposite: true is optional when using references

CReferences allow sharing node_modules between packages

DProject references enable incremental builds in monorepos — TypeScript builds referenced projects first and only rebuilds them when changed

What is declarationMap: true useful for?

javascript

{
  "compilerOptions": {
    "declaration": true,
    "declarationMap": true
  }
}

AdeclarationMap generates a JSON manifest of all exported declarations

BdeclarationMap generates .d.ts.map files that map declaration files back to TypeScript source — enables "Go to Definition" to jump to original .ts source instead of generated .d.ts

CdeclarationMap is a superset of sourceMap — use only one

DdeclarationMap is only needed for external npm packages

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