切记，须在父元素上添加居中属性，如下：
<html> <body> <center><button onClick="myClick()">Hello Word</button></center> <script> function myClick() { alert("123"); } </script> </body> </html>或者：
<html> <body> <div align="center"><button onClick="myClick()">Hello Word</button></div> <script> function myClick(){ alert("123"); } </script> </body> </html>
