Build ESM Modules & Package Boundaries as a system involving module resolution, runtime validation, declaration output, incremental builds, CI, and package boundaries—not only a compiler concern. Remember that TypeScript types are erased at runtime.
Build a Complete Mental Model
Build ESM Modules & Package Boundaries as a system involving module resolution, runtime validation, declaration output, incremental builds, CI, and package boundaries—not only a compiler concern. Remember that TypeScript types are erased at runtime.
Apply It in Production TypeScript
Type-check an original ESM Modules & Package Boundaries example in strict mode, then test valid values, null/undefined, malformed API data, a new union variant, and module boundaries. Fix the contract or validation instead of silencing errors with assertions or any.
After This Lesson
// math.ts
export function add(a: number, b: number) { return a + b; }
// app.ts
import { add } from './math.js';
console.log(add(2, 3));5Try It Yourself
Type-check an original ESM Modules & Package Boundaries example in strict mode, then test valid values, null/undefined, malformed API data, a new union variant, and module boundaries. Fix the contract or validation instead of silencing errors with assertions or any.
Type Safety Warning
Assuming a successful TypeScript compile proves API data and runtime behavior are valid.
Modules Reference — TypeScript