JS vs TS in Node: Quick Differences You’ll See Often

Compile-Time vs Runtime

TypeScript adds static types at compile time. At runtime, the code behaves exactly like JavaScript.

Example Difference

function sum(a: number, b: number): number {
  return a + b;
}

This compiles to:

function sum(a, b) {
  return a + b;
}

No Runtime Type Safety

TypeScript does not validate types at runtime. Use validation libraries for API input validation.

Imports

ES Modules work in both JS and TS, but configuration differs depending on module type.

Production Perspective

Types prevent developer mistakes but do not replace input validation or runtime checks.