Test if two segments intersect

intersect.js

function intersect(a,b,c,d) {
  var a_cd = (d.x - c.x) * (a.y - c.y) > (d.y - c.y) * (a.x - c.x)
  var b_cd = (d.x - c.x) * (b.y - c.y) > (d.y - c.y) * (b.x - c.x)
  var c_ab = (b.x - a.x) * (c.y - a.y) > (b.y - a.y) * (c.x - a.x)
  var d_ab = (b.x - a.x) * (d.y - a.y) > (b.y - a.y) * (d.x - a.x)
  return a_cd !== b_cd && c_ab !== d_ab
}
console.log(intersect({x:0,y:0},{x:1,y:1},{x:1,y:0},{x:0,y:1}))