DevAcademy

1. What is TypeScript?

A completely different language from JavaScriptA typed superset of JavaScript that compiles to plain JavaScriptA JavaScript runtime like Node.jsA CSS framework

2. Do browsers run TypeScript files directly?

Yes, nativelyNo — TypeScript compiles to JavaScript firstOnly Chrome doesOnly with a plugin

3. What happens to TypeScript’s type annotations at runtime?

They are checked again at runtimeThey are erased entirely — compiled JavaScript has no typesThey are converted to commentsThey slow down execution

4. Which command compiles a TypeScript file into JavaScript?

npm run tstscnode --typescriptts-run

5. What does tsconfig.json do?

Stores npm dependenciesConfigures how the TypeScript compiler behaves for the projectReplaces package.jsonRuns tests

6. What does the strict compiler option do?

Disables all type checkingEnables all strict type-checking options at onceOnly checks function return typesSpeeds up compilation

7. How many distinct numeric types does TypeScript have for integers and decimals?

One — number covers bothTwo — int and floatThreeNone, numbers are untyped

8. How do you type an array of strings?

Array<string>()string[]string{}array(string)

9. What does strictNullChecks do?

Disables null entirelyPrevents null/undefined from being assigned to other types unless explicitly allowedOnly affects arraysRemoves the need for type annotations

10. What is the key difference between an array and a tuple in TypeScript?

Tuples cannot hold objectsA tuple has a fixed length with a specific type at each positionArrays are immutable, tuples are notThere is no difference

11. Which of these correctly types a tuple of [string, number]?

string[] & number[][string, number]{string, number}Tuple<string, number>

12. What does a rest element in a tuple, like ...results: number[], allow?

Nothing, it’s invalid syntaxA variable number of trailing elements of that typeOnly one extra elementConverts the tuple into a regular array

13. What value do numeric enum members get by default?

undefinedAuto-incrementing numbers starting at 0Random numbersnull

14. Do string enum members get default values?

Yes, auto-generatedNo, every member must have an explicit valueOnly the first one needs oneYes, they default to their name

15. Unlike interfaces, what happens to a regular enum at compile time?

It’s completely erased like an interfaceIt compiles into a real JavaScript object that exists at runtimeIt becomes a commentIt’s converted into a type alias

16. What is the key difference between any and unknown?

There is no differenceunknown requires narrowing before use, any allows anything with no checksany is safer than unknownunknown cannot hold objects

17. What does the never type represent?

A value that is always undefinedA value that can never occur, e.g. a function that always throwsA boolean that is always falseAn empty array

18. What return type would a function that only logs a message and returns nothing have?

neveranyvoidundefined only

19. Does TypeScript require an explicit annotation for every variable?

Yes, alwaysNo — it can infer types from initial values and contextOnly for numbersOnly inside functions

20. What type is inferred for an array like [1, "two", 3]?

any[](string | number)[]number[]It causes an error

21. What does noImplicitAny do?

Disables all type checkingErrors when a value would otherwise silently be inferred as anyForces every variable to be a union typeOnly applies to function return types

22. What keyword creates a type alias?

interfacetypealiastypedef

23. Can a type alias describe a union of types?

No, only object shapesYes, e.g. type ID = string | numberOnly with interfaceOnly primitive types

24. Does a type alias create a genuinely new, distinct type?

Yes, alwaysNo — it’s just another name for an existing typeOnly for object shapesOnly when exported

25. What does an interface describe?

A specific valueThe shape an object must haveA function’s implementationA CSS class

26. What is structural typing?

Types are matched by name onlyAn object satisfies a type if it has the required shape, regardless of how it was declaredOnly classes can implement interfacesTypes must be explicitly cast

27. How does one interface inherit members from another?

implementsextendsinheritssuper

28. What happens if a parameter has a default value?

It becomes requiredIt becomes optional automatically, using the default when omittedIt must still be passed explicitlyDefault values are not supported

29. What does a rest parameter (...args: number[]) collect?

Only the first extra argumentAny number of remaining arguments into a typed arrayNothing, it’s just documentationOnly string arguments

30. What are function overloads used for?

Making a function run fasterAllowing a function to accept different parameter combinations, each with a precise return typeHiding a function’s implementationOnly usable with arrow functions

31. What does string | number mean for a variable?

It must be both a string and a number at onceIt can be either a string or a numberIt is always a stringIt is invalid syntax

32. What does an intersection type (A & B) require?

The value must be either A or BThe value must satisfy both A and B at onceA and B cannot overlapOnly classes can use intersections

33. What is a discriminated union?

A union with no common propertiesA union of object types sharing a common literal "tag" property, enabling safe narrowingA type that can never be narrowedA special kind of enum

34. What does the literal type "success" allow as a value?

Any stringOnly the exact string "success"Any string containing "success"Numbers only

35. How is a const string variable typically inferred, compared to a let variable?

The same way, as the general string typeconst infers the specific literal type, let infers the broader string typeconst is always anylet cannot hold strings

36. What does the as const assertion do to an object?

Deletes its propertiesLocks it to its most specific literal types and makes it deeply readonlyConverts it to JSONMakes every property optional

TypeScript Beginner Practice

Quick Quiz