creaseLenght.js

class Point {
  constructor(x = 0, y = 0) {
    this.x = x;
    this.y = y;
  }
  set coords({ x = 0, y = 0 }) {
    if (!Number.isNaN(x)) this.x = x;
    if (!Number.isNaN(y)) this.y = y;
  }
  get coords() {
    const { x, y } = this;
    return { x, y };
  }
}

(function crease() {
  const LOOPS = 10 ** 9;
  let len = 0;
  const { sqrt: s, random: r } = Math;
  for (let i = 0; i < LOOPS; i++) {
    // 1. Choose a random point
    const p = new Point(r(), r());

    // 2. Find slope of crease
    const slope = p.y / p.x;
    const m = -1 / slope;

    // 3. Find c of crease
    const mp = new Point(p.x / 2, p.y / 2);
    const c = mp.y - m * mp.x;

    // 4. Find intercept coordinates on left/top edge
    const yInt = new Point();
    if (c >= 0 && c <= 1) yInt.coords = { y: c };
    else yInt.coords = { x: (1 - c) / m, y: 1 };

    // 5. Find intercept coordinates on right/bottom edge
    const xInt = new Point();
    if (-c / m >= 0 && -c / m <= 1) xInt.coords = { x: -c / m };
    else xInt.coords = { x: 1, y: m + c };

    // 6. Calculate distance between the two coordinates
    const dist = s(
      (yInt.coords.x - xInt.coords.x) ** 2 +
        (yInt.coords.y - xInt.coords.y) ** 2
    );

    // 7. Add to the length
    len += dist;
  }

  // 8. Calculate average length
  const avgLen = len / LOOPS;

  // 9. Calculate average percent as compared to max possible crease length
  const percentMaxLen = (avgLen * 100) / s(2);

  // 10. Print result
  console.log(`Average length of crease is: ${avgLen}`);
  console.log(`% max len: ${percentMaxLen}`);
})();