JS에서 사각형을 x, y 좌표로 이동하는 방법

// canvas vars
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
function reOffset(){
    var BB=canvas.getBoundingClientRect();
    offsetX=BB.left;
    offsetY=BB.top;        
}
var offsetX,offsetY;
reOffset();
window.onscroll=function(e){ reOffset(); }
window.onresize=function(e){ reOffset(); }

// animating vars
var pct=101;
var startX,startY,endX,endY,dx,dy;

// canvas styles
ctx.strokeStyle='skyblue';
ctx.fillStyle='blue';

// start animation loop running
requestAnimationFrame(animate);

// listen for mouse events
window.onmousedown=(function(e){handleMouseDown(e);});
window.onmouseup=(function(e){handleMouseUp(e);});

// constantly running loop
// will animate bullet 
function animate(time){
    // return if there's no bullet to animate
    if(++pct>100){requestAnimationFrame(animate);return;}
    // update
    x=startX+dx*pct/100;
    y=startY+dy*pct/100;
    // draw
    ctx.clearRect(0,0,cw,ch);
    ctx.beginPath();
    ctx.moveTo(startX,startY);
    ctx.lineTo(endX,endY);
    ctx.stroke();
    ctx.beginPath();
    ctx.arc(x,y,5,0,Math.PI*2);
    ctx.fill()
    // request another animation loop
    requestAnimationFrame(animate);
}

function handleMouseDown(e){
  // tell the browser we're handling this event
  e.preventDefault();
  e.stopPropagation();
  // save ending position
  startX=parseInt(e.clientX-offsetX);
  startY=parseInt(e.clientY-offsetY);
  // set flag
  pct=101;
}

function handleMouseUp(e){
  // tell the browser we're handling this event
  e.preventDefault();
  e.stopPropagation();
  // save ending position and vector
  endX=parseInt(e.clientX-offsetX);
  endY=parseInt(e.clientY-offsetY);
  dx=endX-startX;
  dy=endY-startY;
  // set pct=0 to start animating
  pct=0;
}

body{ background-color: ivory; }
#canvas{border:1px solid red; }

<h4>Drag the mouse<br>Mousedown sets starting position,<br>Mouseup sets ending position and animates.</h4>
<canvas id="canvas" width=512 height=512></canvas>