HTML DOM Screen 对象
logicalYDPI 属性可返回显示屏幕每英寸的垂直方向的常规点数。
screen.logicalYDPI
<html> <body> <script type="text/javascript"> document.write("<p>Logical YDPI: ") document.write(screen.logicalYDPI + "</p>") </script> </body> </html>