https://twitter.com/gutchom/status/1554756212184399872

example.ts

interface Point {
  x: number;
  y: number;
}

interface Vector {
  x: number;
  y: number;
}

const HorizontalDirections = ["left", "neutral", "right"] as const;
const VerticalDirections = ["top", "neutral", "bottom"] as const;
type HorizontalDirection = typeof HorizontalDirections[number];
type VerticalDirection = typeof VerticalDirections[number];
interface VectorDirection {
  horizontal: HorizontalDirection;
  vertical: VerticalDirection;
}

function vectorFromTwoPoints(prev: Point, curr: Point): Vector {
  return {
    x: curr.x - prev.x,
    y: curr.y - prev.y,
  };
}

function vectorToDirection(vector: Vector): VectorDirection {
  const horizontal = HorizontalDirections[Math.sign(vector.x) + 1];
  const vertical = VerticalDirections[Math.sign(vector.y) + 1];
  return {
    horizontal,
    vertical,
  };
}

function moveDirectionFromTwoPoints(prev: Point, curr: Point): VectorDirection {
  const vector = vectorFromTwoPoints(prev, curr);
  return vectorToDirection(vector);
}

// 目的のやつ
export function detectMoveDirection(
  prevX: number,
  prevY: number,
  currX: number,
  currY: number
) {
  const prev = { x: prevX, y: prevY };
  const curr = { x: currX, y: currY };
  return moveDirectionFromTwoPoints(prev, curr);
}