let hasLeft = true;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  if (mouseX > width/2) {

    if(hasLeft) {

      isRed = !isRed;

      hasLeft = false;

    }

    console.log(hasLeft);

  }

else{

  hasLeft = true;

}

​

  if(isRed) {

    fill('red');

    rect(width/2,0,width/2,height);

  }

}

​