如何在PHP中运行JavaScript代码？（代码示例）

<?php
header("content-type:text/html;charset=utf-8");
echo &#39;<script type="text/javascript">&#39;;
echo &#39;alert("php中文网");&#39;;
echo &#39;</script>&#39;;
?>

<?php
header("content-type:text/html;charset=utf-8");
//php代码
?> 
<script type="text/javascript"> 
    alert("欢迎来到php中文网");
</script>

<?php 
    echo "<div id=&#39;demo&#39;></div>"; 
?> 
<script type="text/JavaScript"> 
  
// 调用函数
var x = myFunction(11, 10);    
document.getElementById("demo").innerHTML = x; 
  
// 函数返回a和b的乘积
function myFunction(a, b) { 
    return a * b;              
} 
</script>