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I have a big group of websites which has an include() on the <head> tag, this include loads the content from a file which contains javascript code, this code uses document.write().

The code on the browser looks something like this:

<html>
<head>
<script>document.write('stuff');</script>
</head>
<body>
content
</body>
</html>

This seems to work fine but I was wondering if it could fail on some browser/puter, since the head tag is before the body tag, and document.write writes to the body tag. Is it possible that document.write would try to write to the body tag when this tag still wasn't loaded?

I have a big group of websites which has an include() on the <head> tag, this include loads the content from a file which contains javascript code, this code uses document.write().

The code on the browser looks something like this:

<html>
<head>
<script>document.write('stuff');</script>
</head>
<body>
content
</body>
</html>

This seems to work fine but I was wondering if it could fail on some browser/puter, since the head tag is before the body tag, and document.write writes to the body tag. Is it possible that document.write would try to write to the body tag when this tag still wasn't loaded?

  • javascript
  • html
  • document.write
Share Improve this question asked Jun 4, 2014 at 18:58 user3571891user3571891 1111 gold badge2 silver badges6 bronze badges 2
  • 3 You could easily make a test case for this, you know – Sterling Archer Commented Jun 4, 2014 at 19:00
  • 2 The best advice to give is not to use document.write. It is considered obsolete and "dangerous" as it by-passes the idea of the DOM. – Ingo Bürk Commented Jun 4, 2014 at 19:03
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2 Answers 2

Reset to default 4

Does document.write from head tag need to wait for window.onload?

No, quite the opposite.

The load event will fire when the document is closed. You can't write to a closed document, so calling write would implicitly call open and erase the existing document.

This seems to work fine but I was wondering if it could fail on some browser/puter, since the head tag is before the body tag, and document.write writes to the body tag.

write will write to whereever the script element is, not to the body.

In this case, however, you are writing text content (which cannot appear as a child node to the head element).

This will cause the head element to end (the end tag is optional) and the body to start (the start tag is optional) and the content to be written at the beginning of the body.

</head> <body> will then be treated as invalid HTML and the browser will do its usual efforts to recover from author errors.

You can see the results in a DOM inspector:

Here is a small test case that shows the answer:

<html>
<head>
<script>
    document.write('stuff'); 
    console.log("document has written from head");</script>
</head>
<body>
<script>
    window.onload = function() {
        console.log("on load function has triggered");
    }
</script>
</body>
</html>

And the output from Chrome Dev Tools console:

document has written from head test.html:3
on load function has triggered test.html:8

So yes, the code in the head section will run before the onload function.

Please note that document.write() is not something you want to be practicing with. In my experience, I've never had to use it. It overwrites the DOM and can be rather nasty if you don't know how it works. You should use the DOM instead.

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