Detect if two lines are intersecting in javascript, if so, return the coordinates of the intersection. Original code in C by Paul Bourke

Line intersection in javascript

// line intercept math by Paul Bourke http://paulbourke.net/geometry/pointlineplane/
// Determine the intersection point of two line segments
// Return FALSE if the lines don't intersect
function intersect(x1, y1, x2, y2, x3, y3, x4, y4) {

  // Check if none of the lines are of length 0
	if ((x1 === x2 && y1 === y2) || (x3 === x4 && y3 === y4)) {
		return false
	}

	denominator = ((y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1))

  // Lines are parallel
	if (denominator === 0) {
		return false
	}

	let ua = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3)) / denominator
	let ub = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3)) / denominator

  // is the intersection along the segments
	if (ua < 0 || ua > 1 || ub < 0 || ub > 1) {
		return false
	}

  // Return a object with the x and y coordinates of the intersection
	let x = x1 + ua * (x2 - x1)
	let y = y1 + ua * (y2 - y1)

	return {x, y}
}