Handle mousedown and mouseup Events with HTML5 Canvas

To handle the mousedown and mouseup event with HTML5 Canvas,

var mouseDown = false;

// for mousedown
canvas1.onmousedown = function(event){
   dragOffset.x = event.x - mainLayer.trans.x;
   dragOffset.y = event.y - mainLayer.trans.y;
   mouseDown = true;
}

// for mouseup
canvas1.onmouseup = function(event){
   if(mouseDown) mouseClick(eevent
   mouseDown = false;
}