blocks|key|1267504|text|因为，至少在HTML4.01和XHTML1(.1)中，<script>元素的type属性是required。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1267505|在HTML+5中，不再需要type。|1267506|事实上，虽然您应该在HTML源中使用text/javascript，但许多服务器都会使用Content-type:+application/javascript发送文件。阅读有关RFC+4329中这些MIME类型的更多信息。|1267507|请注意RFC4329之间的区别，RFC4329将text/javascript标记为过时并建议使用application/javascript，而一些浏览器对包含type="application/javascript"+(在HTML源文件中，而不是发送的文件的HTTP+Content-type头)的<script>元素感到抓狂。最近，WHATWG邮件列表上有一场关于这个差异的讨论(HTML5的type缺省为text/javascript)，请阅读主题为Will+you+consider+about+RFC+4329?的邮件|1267508|entityMap|0|LINK|mutability|MUTABLE|url|http://www.w3.org/TR/html401/interact/scripts.html#adef-type-SCRIPT|1|http://www.whatwg.org/specs/web-apps/current-work/multipage/scripting-1.html#script|2|http://www.ietf.org/rfc/rfc4329.txt|3|http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2010-April/thread.html#25810^0|R|8|12|4|19|8|0|0|D|4|1|6|1|0|I|F|18|10|2H|8|2|0|O|F|1D|M|29|T|47|8|5J|4|5Q|F|6D|X|3|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]]|E|$]]|$1|F|3|G|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|H|3|I|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@$9|1I|A|1J|1|1K]]|E|$]]|$1|J|3|K|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]|$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]]|D|@$9|1Y|A|1Z|1|20]]|E|$]]|$1|L|3|-4|5|6|7|21|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]|T|$5|O|P|Q|E|$R|U]]|V|$5|O|P|Q|E|$R|W]]|X|$5|O|P|Q|E|$R|Y]]]]

Because, at least in HTML 4.01 and XHTML 1(.1), the <code>type</code> attribute for <code>&lt;script&gt;</code> elements is <a href="http://www.w3.org/TR/html401/interact/scripts.html#adef-type-SCRIPT" rel="noreferrer">required</a>.

In <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/scripting-1.html#script" rel="noreferrer">HTML 5</a>, <code>type</code> is no longer required.

In fact, while you should use <code>text/javascript</code> in your HTML source, many servers will send the file with <code>Content-type: application/javascript</code>. Read more about these MIME types in <a href="http://www.ietf.org/rfc/rfc4329.txt" rel="noreferrer">RFC 4329</a>.

Notice the difference between RFC 4329, that marked <code>text/javascript</code> as obsolete and recommending the use of <code>application/javascript</code>, and the reality in which some browsers freak out on <code>&lt;script&gt;</code> elements containing <code>type="application/javascript"</code> (in HTML source, not the HTTP Content-type header of the file that gets send). Recently, there was a discussion on the WHATWG mailing list about this discrepancy (HTML 5's <code>type</code> defaults to <code>text/javascript</code>), read these messages with subject <a href="http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2010-April/thread.html#25810" rel="noreferrer">Will you consider about RFC 4329?</a>

blocks|key|1052918|text|它允许浏览器在请求脚本或样式表之前确定它们是否可以处理脚本/样式语言(或者，在嵌入式脚本/样式的情况下，确定正在使用哪种语言)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1052919|如果浏览器领域的语言之间存在更多的竞争，这将变得更加重要，但VBScript从未超越IE，PerlScript也从未超越IE特定的插件，而JSSS一开始就相当垃圾。|1052920|HTML5草案使该属性成为可选的。|1052921|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

It allows browsers to determine if they can handle the scripting/style language before making a request for the script or stylesheet (or, in the case of embedded script/style, identify which language is being used).

This would be much more important if there had been more competition among languages in browser space, but VBScript never made it beyond IE and PerlScript never made it beyond an IE specific plugin while JSSS was pretty rubbish to begin with.

The draft of HTML5 makes the attribute optional.

blocks|key|1267660|text|Boris+Zbarsky+(Mozilla)可能比其他任何人都更了解壁虎的内部结构，他在http://lists.w3.org/Archives/Public/public-html/2009Apr/0195.html上提供了下面重复的伪代码来描述基于壁虎的浏览器所做的事情：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1267661|if+(@type+not+set+or+empty)+{
+++if+(@language+not+set+or+empty)+{
+++++//+Treat+as+default+script+language;+what+this+is+depends+on+the
+++++//+content-script-type+HTTP+header+or+equivalent+META+tag
+++}+else+{
+++++if+(@language+is+one+of+"javascript",+"livescript",+"mocha",
+++++++++++++++++++++++++++++"javascript1.0",+"javascript1.1",
+++++++++++++++++++++++++++++"javascript1.2",+"javascript1.3",
+++++++++++++++++++++++++++++"javascript1.4",+"javascript1.5",
+++++++++++++++++++++++++++++"javascript1.6",+"javascript1.7",
+++++++++++++++++++++++++++++"javascript1.8")+{
+++++++//+Treat+as+javascript
+++++}+else+{
+++++++//+Treat+as+unknown+script+language;+do+not+execute
+++++}
+++}
}+else+{
+++if+(@type+is+one+of+"text/javascript",+"text/ecmascript",
+++++++++++++++++++++++"application/javascript",
+++++++++++++++++++++++"application/ecmascript",
+++++++++++++++++++++++"application/x-javascript")+{
+++++//+Treat+as+javascript
+++}+else+{
+++++//+Treat+as+specified+(e.g.+if+pyxpcom+is+installed+and
+++++//+python+script+is+allowed+in+this+context+and+the+type
+++++//+is+one+that+the+python+runtime+claims+to+handle,+use+that).
+++++//+If+we+don't+have+a+runtime+for+this+type,+do+not+execute.
+++}
}|code-block|syntax|javascript|1267662|entityMap|0|LINK|mutability|MUTABLE|url|http://lists.w3.org/Archives/Public/public-html/2009Apr/0195.html^0|19|1T|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Boris Zbarsky (Mozilla), who probably knows more about the innards of Gecko than anyone else, provided at <a href="http://lists.w3.org/Archives/Public/public-html/2009Apr/0195.html" rel="noreferrer">http://lists.w3.org/Archives/Public/public-html/2009Apr/0195.html</a> the pseudocode repeated below to describe what Gecko based browsers do:

<pre><code>if (@type not set or empty) {
 if (@language not set or empty) {
 // Treat as default script language; what this is depends on the
 // content-script-type HTTP header or equivalent META tag
 } else {
 if (@language is one of "javascript", "livescript", "mocha",
 "javascript1.0", "javascript1.1",
 "javascript1.2", "javascript1.3",
 "javascript1.4", "javascript1.5",
 "javascript1.6", "javascript1.7",
 "javascript1.8") {
 // Treat as javascript
 } else {
 // Treat as unknown script language; do not execute
 }
 }
} else {
 if (@type is one of "text/javascript", "text/ecmascript",
 "application/javascript",
 "application/ecmascript",
 "application/x-javascript") {
 // Treat as javascript
 } else {
 // Treat as specified (e.g. if pyxpcom is installed and
 // python script is allowed in this context and the type
 // is one that the python runtime claims to handle, use that).
 // If we don't have a runtime for this type, do not execute.
 }
}
</code></pre>

My understanding is that mime types are set by the web server. Why do we add the <code>type="text/javascript</code> or <code>type="text/css"</code> attribute? Isn't this a useless and ignored attribute?

Why write <script type="text/javascript"> when the mime type is set by the server?

服务器

HTML5

我的理解是mime类型是由web服务器设置的。为什么要添加type="text/javascript或type="text/css"属性？这不是一个无用且被忽略的属性吗？

问当mime类型由服务器设置时，为什么还要编写<script type="text/javascript">？
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问当mime类型由服务器设置时，为什么还要编写<script type="text/javascript">？
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