createCanvas(320, 240);

  background(255, 100, 100);

  noStroke();

  fill(100,255,100);

  rect(0,0, 160, 240);

}

​

function draw() {

  console.log( whatside() );

}

​

function whatside() {

  if (mouseX > 160) {

    return "RIGHT";

  } else {

    return "LEFT";

  }

}