Polygon + Point Collision Detection

sketch.js

let polygon = [
  [200, 100], [400, 130], [350, 300], [250, 300]
];

function setup() {
  createCanvas(800, 800);
}

function draw() {
  background(0);

  let collision = false;
  for (let i = 0; i < polygon.length; i++) {
  
    let x1 = polygon[i][0];
    let y1 = polygon[i][1];
    let x2 = polygon[(i + 1) % polygon.length][0];
    let y2 = polygon[(i + 1) % polygon.length][1];

    if (y1 > mouseY != y2 > mouseY && mouseX < (x2 - x1) * (mouseY - y1) / (y2 - y1) + x1 ) {
    
      collision = ! collision;
    }
  }
    
  //console.log(collision);
  //console.log(mouseX, mouseY);

  if (collision) {
    stroke(244, 122, 158);
  }
  else {
    stroke(255, 255, 255);
  }
    
  for (let i = 0; i < polygon.length; i++) {
    line(polygon[i][0], polygon[i][1], polygon[(i+1) % polygon.length][0], polygon[(i+1) % polygon.length][1]);
  }
  

}