Chapter quiz · TypeScript Basics

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8 questions on TypeScript Basics. Pass 70% to clear the chapter.

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Quiz

TS Basics — Chapter Quiz

Eight questions covering primitives, annotations, inference, and type aliases.

0/ 9

Question 1
1
What is the main job of TypeScript at build time?
ARun your codeBCatch type errors before runtimeCMinify your outputDPolyfill old JS features
TS adds a static type checker on top of JS. Its job is to flag type errors at compile time. It doesn't change runtime behavior.
Question 2
2
What type does TS infer for let x = 42?
A42 (literal)BnumberCanyDint
let declarations widen to the primitive type — number here. const x = 42 would keep the literal 42 type.
Question 3
3
Which annotation correctly types a function returning void?
Afunction f(): null { ... }Bfunction f(): void { ... }Cfunction f() void { ... }Dfunction f(): undefined { ... }
void is the return type for "no meaningful return". Note that void differs from undefined in subtle but important ways.
Question 4
4
TS type annotations are emitted in the compiled JavaScript output.
TTrueFFalse
Annotations are erased during compilation. The output is plain JS — types exist only at compile time.
Question 5
5
How do you type an array of strings?
AArray(string)Bstring[] or Array<string>C[string]Dstrings
string[] is the common form. Array<string> is equivalent. [string] is a single-element tuple — different thing.
Question 6
6
The keyword that declares a reusable named type is ___.
type Name = ... gives a name to any type expression. The alternative for object shapes is interface.
Question 7
7
Which of these are TypeScript primitive types?
Select all that apply.
AstringBnumberCbooleanDintEbigint
TS primitives mirror JS — string, number, boolean, bigint, symbol, plus null and undefined. There's no separate int — number covers integers and floats.
Question 8
8
What is the inferred type of colors?
```
const colors = ["red", "green", "blue"];
```
A("red" | "green" | "blue")[]Bstring[]Creadonly ["red", "green", "blue"]DArray<any>
Without as const, an array literal widens to the primitive's array type — string[]. Adding as const would give the narrow tuple type.