//setup y to have the circle begin at the center of the canvas

​

let x=0;

let y=400/2;

let xspeed=8;

​

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(255,0, 0);

    noStroke();

  fill(0,255,200);

  // draw an ellipse halfway from the height of the canvas

  ellipse(x,y,50,50);

    // make the ellipse move to the right side of the canvas

  // upon reaching the far right side of the canvas, the

  // the elispse returns and heads to the left side of the canvas

  // and then moves towards the right side of the canvas upon 

  // hitting the left side.  This continues indefinitly.

  x+=xspeed;

        if (x>width||x<0) xspeed*=-1;

    }