Chapter quiz · Type System Essentials

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8 questions on Type System Essentials. Pass 70% to clear the chapter.

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Quiz

TS Type System Essentials — Chapter Quiz

Eight questions on interfaces, unions, narrowing, and the special types.

0/ 9

Question 1
1
What is the key difference between any and unknown?
Aany is fasterBunknown requires you to narrow before using itCunknown is the same as voidDThey are identical
unknown is the safe top type — you must narrow it before doing anything. any silently disables type checking.
Question 2
2
Which type means a function never returns normally?
AvoidBundefinedCneverDnull
never is the bottom type — functions that always throw or loop forever return never.
Question 3
3
How do you combine two types so the result has all properties of both?
AUnion with |BIntersection with &CExtend with extendsDYou cannot combine types
Intersection (&) merges all properties. Union (|) means "one or the other" — and only common properties are accessible.
Question 4
4
An interface can describe a union type like string | number.
TTrueFFalse
interface only describes object shapes. For unions, you need type X = string | number.
Question 5
5
What does TS infer about x inside the if-block?
```
function f(x: string | number) {
  if (typeof x === "string") {
    // x is ___
  }
}
```
AstringBnumberCstring | numberDany
typeof x === "string" narrows the union — inside the branch TS knows x is string.
Question 6
6
What is a discriminated union's most useful feature?
ASmaller bundle sizeBA shared kind field lets TS narrow per-branch in a switchCThey are mutableDFaster runtime checks
A shared literal kind (or type, or tag) field lets TS narrow each branch of a switch to a specific variant — fully typed access to that variant's fields.
Question 7
7
A function isString(x): x is string is called a type ___.
A type predicate (x is T) tells the compiler the parameter is T when the function returns true.
Question 8
8
Which keywords/modifiers control mutability of a property?
Select all that apply.
AreadonlyBconstCfinalDas const
readonly makes individual properties immutable. as const makes an entire literal deeply readonly. const is for variable bindings, not properties. final isn't a TS keyword.