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var deltaTime  = 0;
var lastTime = Date.now();
(function(){
	deltaTime = (Date.now() - lastTime)/1000  ;
	lastTime = Date.now();
  ctx.fillStyle = "#000";
  ctx.fillRect(0, 0, canvas.width, canvas.height);
  ctx.fillStyle = "#59982f";
  x -= speed * deltaTime;
  ctx.fillRect(x, y, w, 20);
  window.requestAnimationFrame(arguments.callee);
})() 
  
   
  
   
  
  