let x = 0;

​

function setup() {  

   createCanvas(400, 400);

}

​

function draw() {  

   background(0);  

   stroke(255);  

   strokeWeight(4);  

   noFill();  

   ellipse(x, 200, 20, 20); 

  //Checking canvas edges

  if((x>width)||(x<0)){

    speedX *= -1;

  }

  // if(x<0){

  //   speedX = 3;

  // }

x = x + speedX;

}

​