TypeScript vs JavaScript
TypeScript is JavaScript + static types. It catches type errors at compile time but adds a build step. JavaScript is simpler, runs anywhere, but errors appear at runtime. For anything beyond a small script, TypeScript is the better choice.
- TypeScript: any project beyond a small script.
- JavaScript: quick prototypes, scripts, when you can't add a build step.
- TypeScript: simple scripts (overkill).
- JavaScript: large/team codebases (unsafe).
Definition
JavaScript: dynamic types, no build step, runs everywhere, errors at runtime. TypeScript: adds type annotations, compiles to JS, catches errors at compile time, better tooling (autocomplete, refactoring). TypeScript is a superset — all valid JS is valid TS.
Why it exists
JavaScript's flexibility is dangerous at scale — type errors surface in production. TypeScript adds safety and tooling without changing the runtime, making large codebases manageable.
How it works
JavaScript: write .js, run directly. TypeScript: write .ts, tsc compiles to .js (types erased). tsconfig.json configures strictness. Types don't exist at runtime — zero runtime cost.
Scaling limits
TypeScript: build step, learning curve for advanced types, library type defs may be missing. JavaScript: no type safety, harder to refactor, worse tooling.
Cost shape
Both free. TypeScript adds a build step (compile time).
Alternatives
- Just JavaScript — Simpler, no safety.
- JSDoc + checkJs — Types via comments, less power than TS.
Failure modes
- TS: any abuse, complex types. JS: runtime type errors.
- JS: refactoring is risky.
- TS: build complexity.