bouncing balls - js canvas

by Rich Costello

HTML

<h1>bouncing balls</h1>
    <canvas></canvas>

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;
}

JavaScript

// setup canvas

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

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

// function to generate random number

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

// define Ball constructor

function Ball() {
  this.x = random(0,width);
  this.y = random(0,height);
  this.velX = random(-7,7);
  this.velY = random(-7,7);
  this.color = 'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')';
  this.size = random(10,20);
}

// define ball draw method

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

// define ball update method

Ball.prototype.update = function() {
  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;
}

// define ball collision detection

Ball.prototype.collisionDetect = function() {
  for(j = 0; j < balls.length; j++) {
    if( (!(this.x === balls[j].x && this.y === balls[j].y && this.velX === balls[j].velX && this.velY === balls[j].velY)) ) {
      var dx = this.x - balls[j].x;
      var dy = this.y - balls[j].y;
      var 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) +')';
      }
    }
  }
}

// define array to store balls

var balls = [];

// define loop that keeps drawing the scene constantly

function loop() {
  ctx.fillStyle = 'rgba(0,0,0,0.25)';
  ctx.fillRect(0,0,width,height);

  while(balls.length < 25) {
    var ball = new...