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Why don't self-closing script elements work?

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攒了一身酷
攒了一身酷 2020-11-21 04:12

What is the reason browsers do not correctly recognize:
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  • 执笔经年
    2020-11-21 04:50

    Difference between 'true XHTML', 'faux XHTML' and HTML as well as importance of the server-sent MIME type had been already described here well. If you want to try it out right now, here is simple editable snippet with live preview including self-closed script tag for capable browsers:

    div { display: flex; }
div + div {flex-direction: column; }
    <div>Mime type: <label><input type="radio" onchange="t.onkeyup()" id="x" checked  name="mime"> application/xhtml+xml</label>
<label><input type="radio" onchange="t.onkeyup()" name="mime"> text/html</label></div>
<div><textarea id="t" rows="4" 
onkeyup="i.src='data:'+(x.checked?'application/xhtml+xml':'text/html')+','+encodeURIComponent(t.value)"
><?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
[<!ENTITY x "true XHTML">]>
<html xmlns="http://www.w3.org/1999/xhtml">
<body>
  <p>
    <span id="greet" swapto="Hello">Hell, NO :(</span> &x;.
    <script src="data:text/javascript,(g=document.getElementById('greet')).innerText=g.getAttribute('swapto')" />
    Nice to meet you!
    <!-- 
      Previous text node and all further content falls into SCRIPT element content in text/html mode, so is not rendered. Because no end script tag is found, no script runs in text/html
    -->
  </p>
</body>
</html></textarea>

<iframe id="i" height="80"></iframe>

<script>t.onkeyup()</script>
</div>

    You should see Hello, true XHTML. Nice to meet you! below textarea.

    For incapable browsers you can copy content of the textarea and save it as a file with .xhtml (or .xht) extension (thanks Alek for this hint).

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  • 悲&欢浪女
    2020-11-21 04:54

    In case anyone's curious, the ultimate reason is that HTML was originally a dialect of SGML, which is XML's weird older brother. In SGML-land, elements can be specified in the DTD as either self-closing (e.g. BR, HR, INPUT), implicitly closeable (e.g. P, LI, TD), or explicitly closeable (e.g. TABLE, DIV, SCRIPT). XML, of course, has no concept of this.

    The tag-soup parsers used by modern browsers evolved out of this legacy, although their parsing model isn't pure SGML anymore. And of course, your carefully-crafted XHTML is being treated as badly-written SGML-inspired tag-soup unless you send it with an XML mime type. This is also why...

    <p><div>hello</div></p>

    ...gets interpreted by the browser as:

    <p></p><div>hello</div><p></p>

    ...which is the recipe for a lovely obscure bug that can throw you into fits as you try to code against the DOM.

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  • 小鲜肉
    2020-11-21 04:56

    Internet Explorer 8 and earlier do not support XHTML parsing. Even if you use an XML declaration and/or an XHTML doctype, old IE still parse the document as plain HTML. And in plain HTML, the self-closing syntax is not supported. The trailing slash is just ignored, you have to use an explicit closing tag.

    Even browsers with support for XHTML parsing, such as IE 9 and later, will still parse the document as HTML unless you serve the document with a XML content type. But in that case old IE will not display the document at all!

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  • 青春惊慌失措
    2020-11-21 04:59

    The people above have already pretty much explained the issue, but one thing that might make things clear is that, though people use <br/> and such all the time in HTML documents, any / in such a position is basically ignored, and only used when trying to make something both parseable as XML and HTML. Try <p/>foo</p>, for example, and you get a regular paragraph.

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  • 粉色の甜心
    2020-11-21 05:03

    Unlike XML and XHTML, HTML has no knowledge of the self-closing syntax. Browsers that interpret XHTML as HTML don't know that the / character indicates that the tag should be self-closing; instead they interpret it like an empty attribute and the parser still thinks the tag is 'open'.

    Just as <script defer> is treated as <script defer="defer">, <script /> is treated as <script /="/">.

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  • 你的背包
    2020-11-21 05:04

    XHTML 1 specification says:

    С.3. Element Minimization and Empty Element Content

    Given an empty instance of an element whose content model is not EMPTY (for example, an empty title or paragraph) do not use the minimized form (e.g. use <p> </p> and not <p />).

    XHTML DTD specifies script elements as:

    <!-- script statements, which may include CDATA sections -->
<!ELEMENT script (#PCDATA)>
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