body {
  background: #111; 
}

canvas {
  display: block; 
  left: 50%;
  margin: -150px 0 0 -150px;
  position: absolute;
  top: 50%;
}

var c = document.getElementById('c'),
    ctx = c.getContext('2d'),
    cw = c.width = 300,
    ch = c.height = 300,
    parts = [],
    partCount = 200,   
    partsFull = false,    
    hueRange = 50,
    globalTick = 0,
    rand = function(min, max){
        return Math.floor( (Math.random() * (max - min + 1) ) + min);
    };

var Part = function(){
  this.reset();
};

Part.prototype.reset = function(){
  this.startRadius = rand(1, 25);
  this.radius = this.startRadius;
  this.x = cw/2 + (rand(0, 6) - 3);
  this.y = 250;      
  this.vx = 0;
  this.vy = 0;
  this.hue = rand(globalTick - hueRange, globalTick + hueRange);
  this.saturation = rand(50, 100);
  this.lightness = rand(20, 70);
  this.startAlpha = rand(1, 10) / 100;
  this.alpha = this.startAlpha;
  this.decayRate = .1;  
  this.startLife = 7;
  this.life = this.startLife;
  this.lineWidth = rand(1, 3);
}
    
Part.prototype.update = function(){  
  this.vx += (rand(0, 200) - 100) / 1500;
  this.vy -= this.life/50;  
  this.x += this.vx;
  this.y += this.vy;  
  this.alpha = this.startAlpha * (this.life / this.startLife);
  this.radius = this.startRadius * (this.life / this.startLife);
  this.life -= this.decayRate;  
  if(
    this.x > cw + this.radius || 
    this.x < -this.radius ||
    this.y > ch + this.radius ||
    this.y < -this.radius ||
    this.life <= this.decayRate
  ){
    this.reset();  
  }  
};
  
Part.prototype.render = function(){
  ctx.beginPath();
  ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false);
  ctx.fillStyle = ctx.strokeStyle = 'hsla('+this.hue+', '+this.saturation+'%, '+this.lightness+'%, '+this.alpha+')';
  ctx.lineWidth = this.lineWidth;
  ctx.fill();
  ctx.stroke();
};

var createParts = function(){
  if(!partsFull){
    if(parts.length > partCount){
      partsFull = true;
    } else {
      parts.push(new Part()); 
    }
  }
};
  
var updateParts = function(){
  var i = parts.length;
  while(i--){
    parts[i].update();
  }
};

var renderParts = function(){
  var i = parts.length;
  while(i--){
    parts[i].render();
  }   
};
    
var clear = function(){
  ctx.globalCompositeOperation = 'destination-out';
  ctx.fillStyle = 'hsla(0, 0%, 0%, .3)';
  ctx.fillRect(0, 0, cw, ch);
  ctx.globalCompositeOperation = 'lighter';
};
     
var loop = function(){
  window.requestAnimFrame(loop, c);
  clear();
  createParts();
  updateParts();
  renderParts();
  globalTick++;
};

window.requestAnimFrame=function(){return window.requestAnimationFrame||window.webkitRequestAnimationFrame||window.mozRequestAnimationFrame||window.oRequestAnimationFrame||window.msRequestAnimationFrame||function(a){window.setTimeout(a,1E3/60)}}();

loop();