Edit in JSFiddle

window.addEventListener("load", init);

     function init() {
      var stage = new createjs.Stage("myCanvas");
			//
      var ball = new createjs.Shape();
      ball.graphics.beginFill('#888888').drawCircle(0, 0, 30);
      ball.x = stage.canvas.width / 2; // 画面中央に配置
      ball.y = stage.canvas.height / 2;
      stage.addChild(ball);
      var angle = 0;
      var centerScale = 1.0;
      var range = 0.5;
      var speed = 0.05;
      // 時間経過
      createjs.Ticker.addEventListener("tick", handleTick);
      function handleTick() {
        // スケールを変化
        ball.scaleX = ball.scaleY
                = centerScale + Math.sin(angle) * range;
        angle += speed;
        stage.update();
      }
      createjs.Ticker.timingMode = createjs.Ticker.RAF;
    }