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>