TypeScript Interview Preparation
TypeScript is JavaScript with static types. If you know JavaScript, you already know 90% of TypeScript — the remaining 10% is the type system, and that is what interviews test.
Suggested Learning Order
The One-Line Mental Model
TypeScript is a compile-time tool. It erases completely at runtime.
// TypeScript
const add = (a: number, b: number): number => a + b;
// Compiled JavaScript — the types are gone
const add = (a, b) => a + b;Everything follows from this: no runtime type checks, no runtime cost, and no protection from bad API data unless you validate it yourself.
Why Teams Use It
| Problem in plain JavaScript | TypeScript answer |
|---|---|
Cannot read property 'x' of undefined in production | Caught at compile time |
| What shape does this function return? | The type tells you |
| Renaming a field breaks 12 files silently | Compiler lists all 12 |
| Autocomplete guesses | Autocomplete knows |
| Docs go stale | Types are checked documentation |
What It Does NOT Do
- Does not validate data at runtime — an API returning garbage still crashes you
- Does not make code faster
- Does not prevent logic bugs
anysilently disables all of it
Interview Point
The strongest answer to "why TypeScript?" is not "fewer bugs" — it is refactoring confidence and self-documenting interfaces between modules. Any senior interviewer has heard "fewer bugs" a hundred times.
How Deep Do Interviews Go?
For 1–3 years of experience, you need to be fluent in:
typevsinterface- Union and intersection types
- Type narrowing and type guards
- Generics (writing them, not just using them)
- The common utility types
- Typing React props, state, events and hooks
unknownvsanystrictmode and why it matters
You do not need conditional-type wizardry, recursive mapped types, or template literal type gymnastics. If an interview asks for those, they are testing library-author skills, not application skills.