function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(200); 

  percent += 0.005;

  if (percent > 1) percent = 0; 

  var xA = 0; 

  var xB = 400; 

  var px = lerp (xA, xB, percent); 

  ellipse(px, 200, 40, 40); 

}

​

​