PCianes/index.html

## index.html
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Bouncing balls</title>
    <link rel="stylesheet" href="style.css">
</head>
  <body>
    <h1>bouncing balls</h1>
    <canvas></canvas>
    <script src="main.js"></script>
    </body>
</html>

## main.js
// setup canvas

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

const width = canvas.width = window.innerWidth;
const height = canvas.height = window.innerHeight;

// function to generate random number

function random(min,max) {
   const num = Math.floor(Math.random()*(max-min)) + min;
   return num;
}

class Ball {

   constructor(x, y, velX, velY, color, size) {
      this.x = x;
      this.y = y;
      this.velX = velX;
      this.velY = velY;
      this.color = color;
      this.size = size;
   }

   draw() {
      ctx.beginPath();
      ctx.fillStyle = this.color;
      ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
      ctx.fill();
   }

   update() {
      if ((this.x + this.size) >= width) {
         this.velX = -(this.velX);
      }

      if ((this.x - this.size) <= 0) {
         this.velX = -(this.velX);
      }

      if ((this.y + this.size) >= height) {
         this.velY = -(this.velY);
      }

      if ((this.y - this.size) <= 0) {
         this.velY = -(this.velY);
      }

      this.x += this.velX;
      this.y += this.velY;
   }

   collisionDetect() {
      for (let j = 0; j < balls.length; j++) {
         if (!(this === balls[j])) {
            const dx = this.x - balls[j].x;
            const dy = this.y - balls[j].y;
            const distance = Math.sqrt(dx * dx + dy * dy);

            if (distance < this.size + balls[j].size) {
              balls[j].color = this.color = 'rgb(' + random(0, 255) + ',' + random(0, 255) + ',' + random(0, 255) +')';
            }
         }
      }
   }

}

var balls = [];

while (balls.length < 25) {
   const size = random(10,20);
   let ball = new Ball(
      // ball position always drawn at least one ball width
      // away from the edge of the canvas, to avoid drawing errors
      random(0 + size,width - size),
      random(0 + size,height - size),
      random(-5,5),
      random(-5,5),
      'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')',
      size
   );

  balls.push(ball);
}

function loop() {
   ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
   ctx.fillRect(0, 0, width, height);

   for (let i = 0; i < balls.length; i++) {
     balls[i].draw();
     balls[i].update();
     balls[i].collisionDetect();
   }

   requestAnimationFrame(loop);
}

loop();

## style.css
html, body {
  margin: 0;
}

html {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  height: 100%;
}

body {
  overflow: hidden;
  height: inherit;
}

h1 {
  font-size: 2rem;
  letter-spacing: -1px;
  position: absolute;
  margin: 0;
  top: -4px;
  right: 5px;
  color: transparent;
  text-shadow: 0 0 4px white;
}
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8">
	<title>Bouncing balls</title>
	<link rel="stylesheet" href="style.css">
	</head>
	<body>
	<h1>bouncing balls</h1>
	<canvas></canvas>
	<script src="main.js"></script>
	</body>
	</html>
	// setup canvas

	const canvas = document.querySelector('canvas');
	const ctx = canvas.getContext('2d');

	const width = canvas.width = window.innerWidth;
	const height = canvas.height = window.innerHeight;

	// function to generate random number

	function random(min,max) {
	const num = Math.floor(Math.random()*(max-min)) + min;
	return num;
	}

	class Ball {

	constructor(x, y, velX, velY, color, size) {
	this.x = x;
	this.y = y;
	this.velX = velX;
	this.velY = velY;
	this.color = color;
	this.size = size;
	}

	draw() {
	ctx.beginPath();
	ctx.fillStyle = this.color;
	ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
	ctx.fill();
	}

	update() {
	if ((this.x + this.size) >= width) {
	this.velX = -(this.velX);
	}

	if ((this.x - this.size) <= 0) {
	this.velX = -(this.velX);
	}

	if ((this.y + this.size) >= height) {
	this.velY = -(this.velY);
	}

	if ((this.y - this.size) <= 0) {
	this.velY = -(this.velY);
	}

	this.x += this.velX;
	this.y += this.velY;
	}

	collisionDetect() {
	for (let j = 0; j < balls.length; j++) {
	if (!(this === balls[j])) {
	const dx = this.x - balls[j].x;
	const dy = this.y - balls[j].y;
	const distance = Math.sqrt(dx * dx + dy * dy);

	if (distance < this.size + balls[j].size) {
	balls[j].color = this.color = 'rgb(' + random(0, 255) + ',' + random(0, 255) + ',' + random(0, 255) +')';
	}
	}
	}
	}

	}

	var balls = [];

	while (balls.length < 25) {
	const size = random(10,20);
	let ball = new Ball(
	// ball position always drawn at least one ball width
	// away from the edge of the canvas, to avoid drawing errors
	random(0 + size,width - size),
	random(0 + size,height - size),
	random(-5,5),
	random(-5,5),
	'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')',
	size
	);

	balls.push(ball);
	}

	function loop() {
	ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
	ctx.fillRect(0, 0, width, height);

	for (let i = 0; i < balls.length; i++) {
	balls[i].draw();
	balls[i].update();
	balls[i].collisionDetect();
	}

	requestAnimationFrame(loop);
	}

	loop();
	html, body {
	margin: 0;
	}

	html {
	font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
	height: 100%;
	}

	body {
	overflow: hidden;
	height: inherit;
	}

	h1 {
	font-size: 2rem;
	letter-spacing: -1px;
	position: absolute;
	margin: 0;
	top: -4px;
	right: 5px;
	color: transparent;
	text-shadow: 0 0 4px white;
	}