let xspeed = 1;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  xspeed = (mouseX-x) * 0.1;

  x+=xspeed; //mousex - x, can define whether it's on positive or not 

  ellipse (x,height/2,20,20)

}