Calculate the midpoint between two points

JavaScript version
const midpoint = (p1, p2) => [(p1.x + p2.x) / 2, (p1.y + p2.y) / 2];
TypeScript version
interface Point {
x: number;
y: number;
}
const midpoint = (p1: Point, p2: Point): number[] => [(p1.x + p2.x) / 2, (p1.y + p2.y) / 2];