我使用相同的代码来查找相对于特定元素（在本例中为 HTML5 画布）的鼠标位置。这适用于鼠标按下，但会在鼠标抬起时中断。我怎样才能让它在鼠标上工作？
<!DOCTYPE html>
<html>
<body>
<h1>This is page one; here we will play with HTML5</h1>
<a href= "../index.html">This link takes you back to home</a>
<div> <canvas onmousedown="mouseDown()" onmouseup="mouseUp()"
id="myCanvas" width="1600" height="800" style="border:1px solid #000000;">
</canvas> </div>
<script type="text/javascript">
var rect1x = rec1y;
var a = b;
function mouseDown()
{
a = document.getElementById("myCanvas").getBoundingClientRect().left;
b = document.getElementById("myCanvas").getBoundingClientRect().top;
rect1x = window.event.clientX - a;
rect1y = window.event.clientY - b;
}
function mouseUp()
{
var rect2x = window.event.clientX - a;
var rect2y = window.event.clientY - b;
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="#FF0000";
ctx.fillRect(rect1x,rect1y,rect2x,rect2y);
}
</script>
<center><font size=1>Draw!</font></center>
</body>
</html>