TypeScript Fundamentals — Series 2

Preview — 3 of 10 questions

What does this code print?

javascript

enum Direction {
  Up = "UP",
  Down = "DOWN",
}
console.log(Direction.Up);

B"UP"

C"Up"

Dundefined

Does the assignment to point type-check?

javascript

let point: [number, number] = [10, 20];
point = [10, 20, 30];

ACompiles fine — tuples can have extra elements as long as the first ones match

BCompiles fine, but point[2] is undefined at runtime

CType error: a three-element array cannot be assigned to a two-element tuple.

DRuntime error: "too many array elements"

Does this call to greet type-check?

javascript

function greet(name: string, times: number): string {
  return name.repeat(times);
}
greet("Hi", "3");

AType error: the second argument is a string, but times requires a number.

BCompiles fine — TypeScript automatically coerces "3" to the number 3

CCompiles fine because function parameter types are only checked at runtime

DCompile-time error, but only because greet was called with the wrong number of arguments

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