TypeScript Fundamentals — Series 2

Preview — 3 of 10 questions

javascript

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

B"UP"

C"Up"

Dundefined

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

CCompile-time error — a tuple type has a fixed length matching its declared elements, so a third element isn't allowed

DRuntime error: "too many array elements"

javascript

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

ACompile-time error — "3" is a string, which isn't assignable to the declared parameter type 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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