Test if two lines intersect - JavaScript function

Question

I\'ve tried searching for a javascript function that will detect if two lines intersect each other.

The function will take the x,y values of both the start end point

Answer 1

Here comes a TypeScript implementation, heavily inspired by Dan Fox's solution. This implementation will give you the intersection point, if there is one. Otherwise (parallel or no intersection), undefined will be returned.

interface Point2D {
  x: number;
  y: number;
}

function intersection(from1: Point2D, to1: Point2D, from2: Point2D, to2: Point2D): Point2D {
  const dX: number = to1.x - from1.x;
  const dY: number = to1.y - from1.y;

  const determinant: number = dX * (to2.y - from2.y) - (to2.x - from2.x) * dY;
  if (determinant === 0) return undefined; // parallel lines

  const lambda: number = ((to2.y - from2.y) * (to2.x - from1.x) + (from2.x - to2.x) * (to2.y - from1.y)) / determinant;
  const gamma: number = ((from1.y - to1.y) * (to2.x - from1.x) + dX * (to2.y - from1.y)) / determinant;

  // check if there is an intersection
  if (!(0 <= lambda && lambda <= 1) || !(0 <= gamma && gamma <= 1)) return undefined;

  return {
    x: from1.x + lambda * dX,
    y: from1.y + lambda * dY,
  };
}