isolatedModules and Project References

Fast tools (esbuild, SWC, Babel, Vite, Next.js, tsx) compile one file at a time and only strip types. "isolatedModules": true makes TypeScript warn about code that needs information from other files to compile correctly:

• re-exporting a type without export type (export { Product } from "./types"),
• using const enum declared in another file,
• files that are not modules (no import/export).

// with isolatedModules / verbatimModuleSyntax
export type { Product } from "./types";   // correct
export { formatInr } from "./format";       // values are fine

Large repositories split code into several TypeScript projects that build in order. Each referenced project needs "composite": true; tsc --build (tsc -b) only rebuilds what changed.

shopease/
  tsconfig.json          { "files": [], "references": [{ "path": "packages/shared" },
                                                        { "path": "apps/api" }, { "path": "apps/web" }] }
  packages/shared/tsconfig.json   { "compilerOptions": { "composite": true, "outDir": "dist" } }
  apps/api/tsconfig.json          { "references": [{ "path": "../../packages/shared" }] }
  apps/web/tsconfig.json          { "references": [{ "path": "../../packages/shared" }] }

npx tsc -b            # build everything in dependency order
npx tsc -b --watch    # incremental rebuilds