Why is this script element broken up into multiple document.write() calls?

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Why split the <script> tag when writing it with document.write()?

I have frequently seen the following statement:

document.write("<scr");
document.write("ipt language=\"Javascript\" type=\"text/javascript\" src=\"source url\"></scr");
document.write("ipt>");

What is the advantage of this? Why don't people write the whole script, as below?

document.write("<script ");

Would question the jQuery title and tag. Have modified accordingly — James Wiseman, Jul 27 '10 at 09:55
Apologies. Been looking at jQuery all day! Would still argue that 'query' was not an appropriate tag, though. — James Wiseman, Jul 27 '10 at 10:05
Also see http://stackoverflow.com/questions/236073/why-split-the-script-tag-when-writing-it-with-document-write — Crescent Fresh, Jul 27 '10 at 11:58

score 3 · Accepted Answer · answered Jul 27 '10 at 09:53

3

This might help you:

http://www.webmasterworld.com/forum91/2913.htm

Depending on the browser, the amount of other preceding javascript, and how well-formed the overall code is, this is done to prevent the parser from interpreting the and tags as executeable code rather than as a string to be written.

I have found that it just saves headaches down the road if you do this when using script to write script tags.

answered Jul 27 '10 at 09:53

James Wiseman

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Rather than split across multiple *document.write()* calls, it's usually enough to just "invalidate" the closing tag, e.g. ` – Andy E Jul 27 '10 at 10:07

score 2 · Answer 2 · answered Jul 27 '10 at 10:05

This is probably done to comply with the standards – but they did it wrong in this case.

From the description of CDATA data type:

Although the STYLE and SCRIPT elements use CDATA for their data model, for these elements, CDATA must be handled differently by user agents. Markup and entities must be treated as raw text and passed to the application as is. The first occurrence of the character sequence "</" (end-tag open delimiter) is treated as terminating the end of the element's content. In valid documents, this would be the end tag for the element.

So they rather should have split the end-tag open delimiter </ like this:

document.write("<script language=\"Javascript\" type=\"text/javascript\" src=\"source url\"><" + "/script>");

+1 - `<\/script>` works too, so you don't have to use string concatenation. — Andy E, Jul 27 '10 at 10:08
@Andy E: I know. I just used concatenation as well as it was used in the example in the question. — Gumbo, Jul 27 '10 at 10:14

score 1 · Answer 3 · answered Jul 27 '10 at 09:54

1

It depends. When you see such code, it means they are generating certain parts of the page dynamically otherwise yes they could have easily written in <script> tags just below that.

And sometimes, such code is used for malicious purposes.

answered Jul 27 '10 at 09:54

Sarfraz

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score 0 · Answer 4 · answered Jul 27 '10 at 09:53

Isn't this how some people attempt to get past antivirus's script scanners?

To answer your question:
There's no gain from doing this. In fact, it's actually slower, since you're invoking more functions, creating more string objects, and appending more strings.

For older browsers, I guess it might be similar to usage of 

score 0 · Answer 5 · answered Jul 27 '10 at 09:54

I beleive it's some kind of primitive code obfuscation to sneak in script into dynamic pages. If a website filters user input for the string "<script" for example, this piece of code here would still go through.

Most likely this is some attempt to inject malicious code somewehere.

Why is this script element broken up into multiple document.write() calls?

5 Answers5