let x=60;
let y=5;
var Vx=5;
var Vy=5;
function setup() {
createCanvas(500, 400);
}
function draw() {
background(120);
ellipse(x,y,20,20);
x+=Vx;
y+=Vy;
if(x>width||x<0){
Vx*=-1;
}
if(y>height||y<0){
Vy*=-1;
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>