When is a CDATA section necessary within a script tag

Question

Are CDATA tags ever necessary in script tags and if so when   In other words  when and where is this    lt script type  text javascript  gt     lt   CDATA     code         gt   lt  script gt    preferable to this    lt script type  text javascript  gt     code     lt  script gt

User · Accepted Answer

A CDATA section is required if you need your document to parse as XML (e.g. when an XHTML page is interpreted as XML) and you want to be able to write literal i<10 and a && b instead of i<10 and a && b, as XHTML will parse the JavaScript code as parsed character data as opposed to character data by default. This is not an issue with scripts that are stored in external source files, but for any inline JavaScript in XHTML you will probably want to use a CDATA section.

Note that many XHTML pages were never intended to be parsed as XML in which case this will not be an issue.

For a good writeup on the subject, see https://web.archive.org/web/20140304083226/http://javascript.about.com/library/blxhtml.htm

User · Answer

When you want it to validate  in XML XHTML - thanks  Loren Segal

User · Answer

Do not use CDATA in HTML4 but you should use CDATA in XHTML and must use CDATA in XML if you have unescaped symbols like  lt  and

User · Answer

When you want it to validate  in XML XHTML - thanks  Loren Segal

User · Answer

CDATA tells the browser to display the text as is and not to render it as an HTML

User · Answer

It s an X HT ML thing  When you use symbols like  lt  and  gt  within the JavaScript  e g  for comparing two integers  this would have to be parsed like XML  thus they would mark as a beginning or end of a tag   The CDATA means that the following lines  everything up unto the    gt  is not XML and thus should not be parsed that way

User · Answer

When browsers treat the markup as XML    lt script gt   lt   CDATA         code       gt   lt  script gt    When browsers treat the markup as HTML    lt script gt         code     lt  script gt    When browsers treat the markup as HTML and you want your XHTML 1 0 markup  for example  to validate    lt script gt     lt   CDATA         code         gt   lt  script gt

User · Answer

CDATA indicates that the contents within are not XML

User · Answer

That way older browser don t parse the Javascript code and the page doesn t break   Backwards compatability  Gotta love it

User · Answer

CDATA is necessary in any XML dialect  because text within an XML node is treated as a child element before being evaluated as JavaScript  This is also the reason why JSLint complains about the  lt  character in regexes   References   Creating a declarative XML UI language The Future of the Web  Rich Clients  Rich Browsers  Rich Portals

User · Answer

HTML  An HTML parser will treat everything between  lt script gt  and  lt  script gt  as part of the script  Some implementations don t even need a correct closing tag  they stop script interpretation at   lt     which is correct according to the specs       Update In HTML5  and with current browsers  that is not the case anymore    So  in HTML  this is not possible    lt script gt  var x     lt  script gt    alert x   lt  script gt    A CDATA section has no effect at all  That s why you need to write  var x     lt       script gt       or var x     lt   script gt      or similar   This also applies to XHTML files served as text html   Since IE does not support XML content types  this is mostly true    XML  In XML  different rules apply  Note that  non IE  browsers only use an XML parser if the XHMTL document is served with an XML content type   To the XML parser  a script tag is no better than any other tag  Particularly  a script node may contain non-text child nodes  triggered by   lt    and a   amp   sign denotes a character entity   So  in XHTML  this is not possible    lt script gt  if  a lt b  amp  amp  c lt d        alert  Hooray       lt  script gt    To work around this  you can wrap the whole script in a CDATA section  This tells the parser   In this section  don t treat   lt   and   amp   as control characters   To prevent the JavaScript engine from interpreting the   lt   CDATA   and     gt   marks  you can wrap them in comments   If your script does not contain any   lt   or   amp    you don t need a CDATA section anyway

User · Answer

When you are going for strict XHTML compliance  you need the CDATA so less than and ampersands are not flagged as invalid characters

User · Answer

Do not use CDATA in HTML4 but you should use CDATA in XHTML and must use CDATA in XML if you have unescaped symbols like  lt  and

User · Answer

CDATA indicates that the contents within are not XML   Here is an explanation on wikipedia

User · Answer

It to ensure that XHTML validation works correctly when you have JavaScript embedded in your page  rather than externally referenced   XHTML requires that your page strictly conform to XML markup requirements  Since JavaScript may contain characters with special meaning  you must wrap it in CDATA to ensure that validation does not flag it as malformed           With HTML pages on the web you can just include the required JavaScript between  and  tags  When you validate the HTML on your web page the JavaScript content is considered to be CDATA  character data  that is therefore ignored by the validator  The same is not true if you follow the more recent XHTML standards in setting up your web page  With XHTML the code between the script tags is considered to be PCDATA  parsed character data  which is therefore processed by the validator           Because of this  you can t just include JavaScript between the script tags on your page without  breaking  your web page  at least as far as the validator is concerned         You can learn more about CDATA here  and more about XHTML here

User · Answer

to avoid xml errors during xhtml validation

User · Answer

CDATA is necessary in any XML dialect  because text within an XML node is treated as a child element before being evaluated as JavaScript  This is also the reason why JSLint complains about the  lt  character in regexes   References   Creating a declarative XML UI language The Future of the Web  Rich Clients  Rich Browsers  Rich Portals

User · Answer

Do not use CDATA in HTML4 but you should use CDATA in XHTML and must use CDATA in XML if you have unescaped symbols like  lt  and

User · Answer

Basically it is to allow to write a document that is both XHTML and HTML  The problem is that within XHTML  the XML parser will interpret the  amp   lt    characters in the script tag and cause XML parsing error  So  you can write your JavaScript with entities  e g    if  a  amp gt  b  alert  hello world      But this is impractical  The bigger problem is that if you read the page in HTML  the tag script is considered CDATA  by default   and such JavaScript will not run  Therefore  if you want the same page to be OK both using XHTML and HTML parsers  you need to enclose the script tag in CDATA element in XHTML  but NOT to enclose it in HTML   This trick marks the start of a CDATA element as a JavaScript comment  in HTML the JavaScript parser ignores the CDATA tag  it s a comment   In XHTML  the XML parser  which is run before the JavaScript  detects it and treats the rest until end of CDATA as CDATA

User · Answer

It s an X HT ML thing  When you use symbols like  lt  and  gt  within the JavaScript  e g  for comparing two integers  this would have to be parsed like XML  thus they would mark as a beginning or end of a tag   The CDATA means that the following lines  everything up unto the    gt  is not XML and thus should not be parsed that way

User · Answer

Basically it is to allow to write a document that is both XHTML and HTML  The problem is that within XHTML  the XML parser will interpret the  amp   lt    characters in the script tag and cause XML parsing error  So  you can write your JavaScript with entities  e g    if  a  amp gt  b  alert  hello world      But this is impractical  The bigger problem is that if you read the page in HTML  the tag script is considered CDATA  by default   and such JavaScript will not run  Therefore  if you want the same page to be OK both using XHTML and HTML parsers  you need to enclose the script tag in CDATA element in XHTML  but NOT to enclose it in HTML   This trick marks the start of a CDATA element as a JavaScript comment  in HTML the JavaScript parser ignores the CDATA tag  it s a comment   In XHTML  the XML parser  which is run before the JavaScript  detects it and treats the rest until end of CDATA as CDATA

User · Answer

Do not use CDATA in HTML4 but you should use CDATA in XHTML and must use CDATA in XML if you have unescaped symbols like  lt  and

User · Answer

HTML  An HTML parser will treat everything between  lt script gt  and  lt  script gt  as part of the script  Some implementations don t even need a correct closing tag  they stop script interpretation at   lt     which is correct according to the specs       Update In HTML5  and with current browsers  that is not the case anymore    So  in HTML  this is not possible    lt script gt  var x     lt  script gt    alert x   lt  script gt    A CDATA section has no effect at all  That s why you need to write  var x     lt       script gt       or var x     lt   script gt      or similar   This also applies to XHTML files served as text html   Since IE does not support XML content types  this is mostly true    XML  In XML  different rules apply  Note that  non IE  browsers only use an XML parser if the XHMTL document is served with an XML content type   To the XML parser  a script tag is no better than any other tag  Particularly  a script node may contain non-text child nodes  triggered by   lt    and a   amp   sign denotes a character entity   So  in XHTML  this is not possible    lt script gt  if  a lt b  amp  amp  c lt d        alert  Hooray       lt  script gt    To work around this  you can wrap the whole script in a CDATA section  This tells the parser   In this section  don t treat   lt   and   amp   as control characters   To prevent the JavaScript engine from interpreting the   lt   CDATA   and     gt   marks  you can wrap them in comments   If your script does not contain any   lt   or   amp    you don t need a CDATA section anyway

User · Answer

CDATA indicates that the contents within are not XML   Here is an explanation on wikipedia

User · Answer

When browsers treat the markup as XML    lt script gt   lt   CDATA         code       gt   lt  script gt    When browsers treat the markup as HTML    lt script gt         code     lt  script gt    When browsers treat the markup as HTML and you want your XHTML 1 0 markup  for example  to validate    lt script gt     lt   CDATA         code         gt   lt  script gt

User · Answer

CDATA tells the browser to display the text as is and not to render it as an HTML

User · Answer

When you are going for strict XHTML compliance  you need the CDATA so less than and ampersands are not flagged as invalid characters

User · Answer

When browsers treat the markup as XML    lt script gt   lt   CDATA         code       gt   lt  script gt    When browsers treat the markup as HTML    lt script gt         code     lt  script gt    When browsers treat the markup as HTML and you want your XHTML 1 0 markup  for example  to validate    lt script gt     lt   CDATA         code         gt   lt  script gt

User · Answer

When you want it to validate  in XML XHTML - thanks  Loren Segal

User · Answer

to avoid xml errors during xhtml validation

User · Answer

When you are going for strict XHTML compliance  you need the CDATA so less than and ampersands are not flagged as invalid characters

User · Answer

When you want it to validate  in XML XHTML - thanks  Loren Segal

User · Answer

When browsers treat the markup as XML    lt script gt   lt   CDATA         code       gt   lt  script gt    When browsers treat the markup as HTML    lt script gt         code     lt  script gt    When browsers treat the markup as HTML and you want your XHTML 1 0 markup  for example  to validate    lt script gt     lt   CDATA         code         gt   lt  script gt

User · Answer

When you are going for strict XHTML compliance  you need the CDATA so less than and ampersands are not flagged as invalid characters

User · Answer

It to ensure that XHTML validation works correctly when you have JavaScript embedded in your page  rather than externally referenced   XHTML requires that your page strictly conform to XML markup requirements  Since JavaScript may contain characters with special meaning  you must wrap it in CDATA to ensure that validation does not flag it as malformed           With HTML pages on the web you can just include the required JavaScript between  and  tags  When you validate the HTML on your web page the JavaScript content is considered to be CDATA  character data  that is therefore ignored by the validator  The same is not true if you follow the more recent XHTML standards in setting up your web page  With XHTML the code between the script tags is considered to be PCDATA  parsed character data  which is therefore processed by the validator           Because of this  you can t just include JavaScript between the script tags on your page without  breaking  your web page  at least as far as the validator is concerned         You can learn more about CDATA here  and more about XHTML here

User · Answer

CDATA indicates that the contents within are not XML

User · Answer

That way older browser don t parse the Javascript code and the page doesn t break   Backwards compatability  Gotta love it

[javascript] When is a CDATA section necessary within a script tag?

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