29 lines, no comments · 1,750 tokens, written in 9 seconds for $0.0037

 1  let x, y;
 2  let xs, ys;
 3  let col;
 4  
 5  function setup() {
 6    createCanvas(600, 400);
 7    x = width / 2;
 8    y = height / 2;
 9    xs = 4;
10    ys = 3;
11    col = color(255, 0, 0);
12  }
13  
14  function draw() {
15    background(20);
16    fill(col);
17    noStroke();
18    ellipse(x, y, 50, 50);
19    x += xs;
20    y += ys;
21    if (x > width - 25 || x < 25) {
22      xs *= -1;
23      col = color(random(255), random(255), random(255));
24    }
25    if (y > height - 25 || y < 25) {
26      ys *= -1;
27      col = color(random(255), random(255), random(255));
28    }
29  }