Type System Basics — Series 3

Preview — 3 of 10 questions

Which declaration correctly annotates both parameters and the return type?

javascript

function add(a: number, b: number): number {
  return a + b;
}

Afunction add(a, b): number, number { return a + b; }

Bfunction add(a: number, b: number): number { return a + b; }

Cfunction add(a, b) : (number, number) => number { return a + b; }

Dfunction add<number>(a, b) { return a + b; }

What are the inferred types of a and b?

javascript

const a = "hello";
let b = "hello";

ABoth are string

BBoth are "hello"

Ca is string, b is "hello"

Da is "hello", b is string

What is the inferred type of mixed?

javascript

const mixed = [1, "two", 3];

A(string | number)[]

Bany[]

C[number, string, number]

Dnumber[], with "two" reported as an error

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