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8 questions on Functions & Inference. Pass 70% to clear the chapter.

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TS Functions & Inference — Chapter Quiz

Eight questions on function types, parameters, overloads, and inference.

0/ 8

Question 1
1
What is the function type expression for a function that takes a string and returns a number?
Afunction(string): numberB(s: string) => numberC(string) -> numberDfn<string, number>
(s: string) => number is the arrow form used everywhere for function types.
Question 2
2
How do you mark a function parameter as optional?
AAdd a ? after the parameter nameBGive it a default valueCUse optional<T>DBoth A and B
Either name?: T (optional, possibly undefined) or name: T = default (default value makes it optional too).
Question 3
3
TS can infer the return type of a function — you don't have to annotate it.
TTrueFFalse
TS infers return types from the body. Public API surfaces often benefit from explicit annotations as documentation and to prevent accidental signature changes.
Question 4
4
What does the void return type mean for a callback?
AThe callback must return undefinedBThe callback may return any value, but the caller will ignore itCThe callback cannot returnDThe callback throws
A void return in a callback type means the caller ignores the return value — the callback is free to return anything.
Question 5
5
What is the inferred return type of add?
```
function add(a: number, b: number) {
  return a + b;
}
```
AanyBnumberCunknownDvoid
TS infers number from the body. The annotation on the return value is optional here.
Question 6
6
What is a rest parameter typed as?
AA single valueBAn array of the element typeCAn objectDA union
function f(...nums: number[]) — the rest parameter collects arguments into an array of the element type.
Question 7
7
When you declare multiple function signatures for the same name, the pattern is called function ___.
Overload signatures let one function accept different argument shapes — the implementation must be compatible with all of them.
Question 8
8
Which special parameter slot is used to type the value of this inside a method?
AThe first regular parameterBA fake first parameter named thisCYou cannot type thisDA generic type parameter
function f(this: SomeType, ...) — the this parameter is erased at runtime but type-checks the value of this inside the function body.