How to change mouse over to onclick

How can I change this code instead of dragging you just click two elements to exchange the position of the two elements? I wanted to exchange two tiles through clicking one then another but instead, in here you need to drag the first tile to bring it to the other then they will exchange.

  function onPuzzleClick(e){
        if(e.layerX || e.layerX == 0){
            _mouse.x = e.layerX - _canvas.offsetLeft;
            _mouse.y = e.layerY - _canvas.offsetTop;
        }
        else if(e.offsetX || e.offsetX == 0){
            _mouse.x = e.offsetX - _canvas.offsetLeft;
            _mouse.y = e.offsetY - _canvas.offsetTop;
        }
        _currentPiece = checkPieceClicked();
        if(_currentPiece != null){
            _stage.clearRect(_currentPiece.xPos,_currentPiece.yPos,pcWidth,pcHeight);
            _stage.save();
            _stage.globalAlpha = .9;
            _stage.drawImage(_img, _currentPiece.sx, _currentPiece.sy, pcWidth, pcHeight, _mouse.x - (pcWidth / 2), _mouse.y - (pcHeight / 2), pcWidth, pcHeight);
            _stage.restore();
            document.onmousemove = updatePuzzle;
            document.onmouseup = pieceDropped;
        }
    }
    function checkPieceClicked(){
        var i;
        var piece;
        for(i = 0;i < _pieces.length;i++){
            piece = _pieces[i];
            if(_mouse.x < piece.xPos || _mouse.x > (piece.xPos + pcWidth) || _mouse.y < piece.yPos || _mouse.y > (piece.yPos + pcHeight)){
                //PIECE NOT HIT
            }
            else{
                return piece;
            }
        }
        return null;
    }
    function updatePuzzle(e){
        _currentDropPiece = null;
        if(e.layerX || e.layerX == 0){
            _mouse.x = e.layerX - _canvas.offsetLeft;
            _mouse.y = e.layerY - _canvas.offsetTop;
        }
        else if(e.offsetX || e.offsetX == 0){
            _mouse.x = e.offsetX - _canvas.offsetLeft;
            _mouse.y = e.offsetY - _canvas.offsetTop;
        }
        _stage.clearRect(0,0,width,height);
        var i;
        var piece;
        for(i = 0;i < _pieces.length;i++){
            piece = _pieces[i];
            if(piece == _currentPiece){
                continue;
            }
            _stage.drawImage(_img, piece.sx, piece.sy, pcWidth, pcHeight, piece.xPos, piece.yPos, pcWidth, pcHeight);
            _stage.strokeRect(piece.xPos, piece.yPos, pcWidth,pcHeight);
            if(_currentDropPiece == null){
                if(_mouse.x < piece.xPos || _mouse.x > (piece.xPos + pcWidth) || _mouse.y < piece.yPos || _mouse.y > (piece.yPos + pcHeight)){
                    //NOT OVER
                }
                else{
                    _currentDropPiece = piece;
                    _stage.save();
                    _stage.globalAlpha = .4;
                    _stage.fillStyle = PUZZLE_HOVER_TINT;
                    _stage.fillRect(_currentDropPiece.xPos,_currentDropPiece.yPos,pcWidth, pcHeight);
                    _stage.restore();
                }
            }
        }
        _stage.save();
        _stage.globalAlpha = .6;
        _stage.drawImage(_img, _currentPiece.sx, _currentPiece.sy, pcWidth, pcHeight, _mouse.x - (pcWidth / 2), _mouse.y - (pcHeight / 2), pcWidth, pcHeight);
        _stage.restore();
        _stage.strokeRect( _mouse.x - (pcWidth / 2), _mouse.y - (pcHeight / 2), pcWidth,pcHeight);
    }
    function pieceDropped(e){
        document.onmousemove = null;
        document.onmouseup = null;
        if(_currentDropPiece != null){
            var tmp = {xPos:_currentPiece.xPos,yPos:_currentPiece.yPos};
            _currentPiece.xPos = _currentDropPiece.xPos;
            _currentPiece.yPos = _currentDropPiece.yPos;
            _currentDropPiece.xPos = tmp.xPos;
            _currentDropPiece.yPos = tmp.yPos;

Here’s how to swap pieces using mouse clicks instead of drags

In the mouseup handler:

Check if the user hit any piece.
If the user hit a piece and no piece was previously “selected”, then “select” this piece.
If the user hit a piece and there was as previous selection, then swap the 2 pieces and reset the pieces.
If the user clicks outside of all pieces, clear any “selected” piece.

Here is working code for you to look at and a Fiddle: http://jsfiddle.net/m1erickson/a75xz/

<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>

<style>
    body{ background-color: ivory; }
    canvas{border:1px solid red;}
</style>

<script>
$(function(){

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");
    var canvasOffset=$("#canvas").offset();
    var offsetX=canvasOffset.left;
    var offsetY=canvasOffset.top;
    var canvasWidth=canvas.width;
    var canvasHeight=canvas.height;

    // create "pieces"
    var selectedPiece=-1;
    var pieceSize=75;
    var pieces=[];
    pieces.push({x:50,y:30,color:"orange"});
    pieces.push({x:150,y:30,color:"green"});
    pieces.push({x:250,y:30,color:"blue"});
    for(var x=0;x<pieces.length;x++){
        drawPiece(x,false);
    }

    // draw the specified piece
    // stroke it in red if it's selected
    function drawPiece(pieceId,isStroked){
        if(pieceId<0){return;}
        var piece=pieces[pieceId];
        ctx.save();
        ctx.beginPath();
        ctx.fillStyle=piece.color;
        ctx.rect(piece.x,piece.y,pieceSize,pieceSize);
        ctx.fill();
        ctx.strokeStyle=(isStroked ? "red" : "black");
        ctx.lineWidth=6;
        ctx.stroke();
        ctx.fillStyle="white";
        ctx.font = 'italic 18px Calibri';
        ctx.fillText("Box#"+pieceId,piece.x+15,piece.y+25);
        ctx.restore();
    }

    function hitTest(x,y){
        var hit=-1;
        for(var pieceId=0;pieceId<pieces.length;pieceId++){
            piece=pieces[pieceId];
            var isHit=!(x<piece.x || x>(piece.x + pieceSize) || y<piece.y || y>(piece.y + pieceSize));
            if(isHit){
                hit=pieceId;
                break; // Hit! We're outta here...   
            }
        }
        return(hit); // returns piece# if hit else -1 to indicate no hits
    }

    function handleMouseUp(e){
      canMouseX=parseInt(e.clientX-offsetX);
      canMouseY=parseInt(e.clientY-offsetY);

      // de-highlight previous selection, if any
      drawPiece(selectedPiece,false)

      // did we hit a piece?
      var hit=hitTest(canMouseX,canMouseY);

      // if no-hit, the user clicked outside a box
      // so clear the selectedPiece and we're outta here
      if(hit<0){
          drawPiece(selectedPiece,false)
          selectedPiece=-1;
          return;
      }

      // Hit!
      // if no previous selection, 
      // set selectedPiece and highlight selectedPiece
      if(selectedPiece<0){
              selectedPiece=hit;
              drawPiece(selectedPiece,true);
      }
      // else, there was a piece already selected
      // so swap these pieces!
      else{
          var s=pieces[selectedPiece];
          var h=pieces[hit];
          var temp={x:s.x, y:s.y}; 
          s.x=h.x;
          s.y=h.y;
          h.x=temp.x;
          h.y=temp.y;
          drawPiece(selectedPiece,false);
          drawPiece(hit,false);
          selectedPiece=-1; // clear 
      }

    }  // end handleMouseDown()

    $("#canvas").mouseup(function(e){handleMouseUp(e);});


}); // end $(function(){});
</script>

</head>

<body>
    <br/><p>Click once to select a box</p>
    <p>Click a second box to swap the boxes</p>
    <canvas id="canvas" width=400 height=300></canvas>
</body>
</html>