HTML5 Relative Dual Animation

<!DOCTYPE HTML>
<html>
  <head>
    <style>
      body {
        margin: 0px;
        padding: 0px;
      }
    </style>
  </head>
  <body>
    <canvas id="myCanvas" width="578" height="200"></canvas>
    <script>
      window.requestAnimFrame = (function(callback) {
        return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
        function(callback) {
          window.setTimeout(callback, 1000 / 60);
        };
      })();

        function moveSquare(mySquare, newX, newY) {
            mySquare.x = mySquare.x + newX;
            mySquare.y += newY;

        }


      function drawRectangle(myRectangle, mySquare, context) {
        //context.beginPath();
        context.fillStyle = 'rgb(0,0,255)';
        context.fillRect(mySquare.x, mySquare.y, mySquare.width, mySquare.height);
        context.fillStyle = 'rgba(255,0,0,0.5)';
        context.fillRect(myRectangle.x, myRectangle.y, myRectangle.width, myRectangle.height);
        context.fill();
        context.lineWidth = myRectangle.borderWidth;
        context.strokeStyle = 'black';
        context.stroke();
      }
      function animate(myRectangle, mySquare, canvas, context, startTime) {
        // update
        var time = (new Date()).getTime() - startTime;

        var linearSpeed = 100;
        // pixels / second
        var newX = linearSpeed * time / 1000;

        if(newX < canvas.width - myRectangle.width - myRectangle.borderWidth / 2) {
          myRectangle.x = newX;
        }
                  if(mySquare.x < myRectangle.x - mySquare.width) {
          moveSquare(mySquare, .75, 0);
        }


        // clear
        context.clearRect(0, 0, canvas.width, canvas.height);

        drawRectangle(myRectangle, mySquare, context);

        // request new frame
        requestAnimFrame(function() {
          animate(myRectangle, mySquare, canvas, context, startTime);
        });
      }
      var canvas = document.getElementById('myCanvas');
      var context = canvas.getContext('2d');

      var myRectangle = {
        x: 0,
        y: 75,
        width: 100,
        height: 50,
        borderWidth: 5
      };

      var mySquare = {
        x:200,
        y:75,
        width: 50,
        height: 50,
        borderWidth: 5
      }


var startTime = (new Date()).getTime();
        //r go = true;
//    while(go) {
            animate(myRectangle, mySquare, canvas, context, startTime);
  // }

      // wait one second before starting animation

    </script>
  </body>
</html>