How to handle mousedown and mouseup 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; }