36 lines, 1 of them comments · 382 tokens, written in 3 seconds for $0.0033

 1  let circles = [];
 2  let numCircles = 10;
 3  
 4  function setup() {
 5    createCanvas(600, 400);
 6    for (let i = 0; i < numCircles; i++) {
 7      circles.push({
 8        x: random(width),
 9        y: random(height),
10        r: random(30, 60),
11        dx: random(-3, 3),
12        dy: random(-3, 3),
13        color: [random(255), random(255), random(255)]
14      });
15    }
16  }
17  
18  function draw() {
19    background(30, 36, 50, 60);
20    for (let c of circles) {
21      fill(c.color[0], c.color[1], c.color[2], 180);
22      noStroke();
23      ellipse(c.x, c.y, c.r);
24      c.x += c.dx;
25      c.y += c.dy;
26      // Bounce off walls
27      if (c.x - c.r/2 < 0 || c.x + c.r/2 > width) {
28        c.dx *= -1;
29        c.color = [random(255), random(255), random(255)];
30      }
31      if (c.y - c.r/2 < 0 || c.y + c.r/2 > height) {
32        c.dy *= -1;
33        c.color = [random(255), random(255), random(255)];
34      }
35    }
36  }