php有办法实现像这样输出js代码？该怎么解决

php有办法实现像这样输出js代码？
比如有个变量值是这样的

PHP code

<!--

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-->$a = "<script>window.location.href='http://xxx.com';</script>";

在网页上是直接显示但不执行js：

Assembly code

<!--

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--><script>window.location.href='http://xxx.com';</script>

查看html源文件是这样：

HTML code

<!--

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http://www.CodeHighlighter.com/

--><script>window.location.href='http://xxx.com';</script>

php有这种函数？还是要怎么转换？

------解决方案--------------------
echo htmlentities($a);
------解决方案--------------------
你这个是网页表单提交的吧？提交处理的代码里有过滤。
------解决方案--------------------

PHP code

$a = "<script>window.location.href='http://xxx.com';</script>";
$b = htmlspecialchars($a);
echo $b;
//result: <script>window.location.href='http://xxx.com';</script> 
//source: <script>window.location.href='http://xxx.com';</script> <div class="clear">
                 
              
              
        
            </div>