html - Can't run JavaScript in CDATA

I am trying to run following HTML in every browser: Opera, FF, IE, Chrome

<!DOCTYPE html  PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" ".dtd">
<html xmlns="" xml:lang="en" lang="en">
 <head>
  <meta http-equiv="Content-Type" content="application/xhtml+xml; charset=utf-8">
 </head>
 <body>
  <script>
  <![CDATA[
     alert('Hey!');
  ]]>
  </script>
 </body>
</html>

None of them display the alert. Chrome logs an error in console: Uncaught SyntaxError: Unexpected token <. It seems to be complaining about the fist < in CDATA declaration. Firefox also logs "syntax error"

The w3schools point out that this is the way to use CDATA .asp. Other answers on this site suggest it. What am I doing wrong? I tried playing with namespaces and doctypes, but that did not change anything.

Edit: I added XHTML name space and doctype, that I originally removed and the problem still persists.

I am trying to run following HTML in every browser: Opera, FF, IE, Chrome

<!DOCTYPE html  PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
 <head>
  <meta http-equiv="Content-Type" content="application/xhtml+xml; charset=utf-8">
 </head>
 <body>
  <script>
  <![CDATA[
     alert('Hey!');
  ]]>
  </script>
 </body>
</html>

The w3schools point out that this is the way to use CDATA http://www.w3schools.com/xml/xml_cdata.asp. Other answers on this site suggest it. What am I doing wrong? I tried playing with namespaces and doctypes, but that did not change anything.

Edit: I added XHTML name space and doctype, that I originally removed and the problem still persists.

Share Improve this question edited May 23, 2017 at 12:30 CommunityBot 11 silver badge asked Mar 6, 2012 at 19:25 Mike Starov 7,2967 gold badges38 silver badges37 bronze badges

1 XML != HTML. Here is a question that explains it: – Pekka Commented Mar 6, 2012 at 19:26
1 possible duplicate of When is a CDATA section necessary within a script tag? – Pekka Commented Mar 6, 2012 at 19:27
1 XHTML is XML. In fact all HTML on my server is generated by XSL templates, so by definition it is valid XML. – Mike Starov Commented Mar 6, 2012 at 19:28
but that doesn't automatically make it X(HT)ML. Are you using an explicit XHTML doctype? – Pekka Commented Mar 6, 2012 at 19:30
Yes. But that does not change the outcome. All browsers still complain about syntax error. – Mike Starov Commented Mar 6, 2012 at 19:32

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5 Answers 5

Sorted by: Reset to default 7

The difference is between HTML and XHTML. W3Schools is correct that it’s a valid CDATA construct within XHTML, but as your question indicates that your code is HTML and there is no such thing as CDATA inside a <script> in HTML, your example fails as soon as the interpreter sees the "<". You can tell the browser that it’s looking at XHTML, but it's probably safer to handle HTML, too. To do that, you need to hide the CDATA inside JavaScript comments. (You might also consider identifying which language is inside your <script> block.)

<html>
 <head>
 </head>
 <body>
  <script>
  //<![CDATA[
     alert('Hey!');
  //]]>
  </script>
 </body>
</html>

This is, in fact, the method recommended by the World Wide Web Consortium (W3C) in XHTML Media Types, A.4. Embedded Style Sheets and Scripts.

The related question When is a CDATA section necessary within a script tag? explains that a CDATA section is recommended when embedding scripts in XHTML documents. However, just setting a XHTML doctype to the test document isn't enough. The CDATA is still being treated as a syntax error.

According to this blog post, that is because the content type needs to match the doctype definition. Proper XHTML needs to have the following Content-type header set:

Content-type: application/xhtml+xml

if that is not specified and text/html sent instead, browsers will revert to HTML. And indeed, if I add that header to my test case, browsers start properly parsing the JavaScript inside the CDATA even when the CDATA it's not commented out.

This works for me (setting the header using PHP):

<?php header("Content-type: application/xhtml+xml"); 
      echo '<?xml version="1.0" encoding="UTF-8"?>'; ?>
<!DOCTYPE html  PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
  <head>
    <script><![CDATA[alert('Hey!');]]></script>
  </head>
  <body>
  </body>
 </html>

You may see it as XML (XHTML) but that's not how the browser sees it.

You're serving it a text/html which means that the browser sees it as HTML.

It needs to be served with an XML mime type such as application/xhtml+xml

i.e. like this

http://www.alohci.net/application/xhtml+xml/starov.htm.ashx

and not like this

http://www.alohci.net/text/html/starov.htm.ashx

Check the view source to see that it's the same file. Check the "Net" tab in firebug (or the equivalent for your browser) to see the content type in the response headers.

Also, you need to comment out the CDATA so it won't throw a parsing error when it's run:

<script>
//<![CDATA[
     alert('Hey!');
//]]>
</script>

1) Comment your CDATA

  //<![CDATA[
     alert('Hey!');
  //]]>

2) add a script type

<script type="text/javascript">

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5 Answers 5

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