blocks|key|1274403|text|在文档中的任何位置都会执行JavaScript。如果您将内联JavaScript放在正文中，当浏览器访问到它时，它将被执行。如果您使用$(document).ready(...)来执行任务，那么位置应该无关紧要。否则，您可能会发现重要的角落案例。一般来说，这无关紧要。脚本以head标记结尾，这在很大程度上打破了传统。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1274404|entityMap^0|1V|M|3T|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

JavaScript is executed wherever it is found in the document. If you place inline JavaScript in the body, it will be executed when the browser comes to it. If you're using <code>$(document).ready(...)</code> to execute things, then the positioning shouldn't matter. Otherwise, you may find corner cases where it matters. In general, it does not matter. Scripts end up in the <code>head</code> tag mostly out of tradition.

blocks|key|1489235|text|当浏览器读取脚本标记时，一切都会停止，直到它处理完它为止。因此，如果尽可能向下移动脚本标记-理想情况下就在结束正文标记之前，页面将呈现得更快。显然，总的加载时间是相同的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1489236|当然，在包含jQuery之前，您必须确保不会实际调用任何jQuery函数。|1489237|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Everything stops when the browser reads a script tag until it has processed it. Your page will therefore render quicker if you move the script tags down as far as possible - ideally just before the end body tag. Obviously the total load time will be the same.

You will have to make sure you don't actually call any jQuery functions until jQuery is included of course.

blocks|key|1274522|text|基本上，浏览器会停止呈现页面，直到.js文件完全下载并处理完毕。由于它们会随着超文本标记语言的到来而逐步呈现页面，因此引用的.js文件越晚，用户体验就越好。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1274523|因此，诀窍是在head中只包含绝对关键的脚本，并在页面末尾加载其余脚本。|1274524|entityMap^0|H|3|1Q|3|0|7|4|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

Basically, browsers stop rendering page until <code>.js</code> files are completely downloaded and processed. Since they render page progressively as HTML arrives, the later <code>.js</code> files are referenced, the better user experience will be.

So the trick is to include only absolutely crucial scripts in the <code>head</code>, and load remaining ones towards the end of the page.

blocks|key|1274552|text|它可以放在head或body标记中。请记住，它将在每次读取时执行，而不一定是在文档加载完成时执行。看看here吧。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1274553|entityMap|0|LINK|mutability|MUTABLE|url|http://www.w3schools.com/js/js_whereto.asp^0|5|4|A|4|1F|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

It can go in the <code>head</code> or <code>body</code> tag. Just keep in mind that it will execute whenever is read and not necessarily when the document is finished loading. Take a look <a href="http://www.w3schools.com/js/js_whereto.asp" rel="nofollow noreferrer">here</a>.

blocks|key|1274599|text|不，它可以在任何地方。事实上，有时把它放在文档的底部是个好主意。有关原因的解释，请参阅http://developer.yahoo.com/performance/rules.html#js_bottom。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1274600|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.yahoo.com/performance/rules.html#js_bottom^0|17|1N|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

No, it can be anywhere. In fact, it’s sometimes a good idea to put it at the bottom of the document. For an explanation why, see <a href="http://developer.yahoo.com/performance/rules.html#js_bottom" rel="noreferrer">http://developer.yahoo.com/performance/rules.html#js_bottom</a>.

blocks|key|1274644|text|实际上，出于性能原因，您几乎总是希望将脚本标记放在页面的底部。为什么？您希望先加载页面结构和CSS，以便用户可以立即看到页面。然后，您希望所有行为驱动的代码最后加载。YSlow是一个很好的火狐扩展，它会给你的性能打分。它给你打分的项目之一是你的javascript是否在底部而不是顶部。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1274645|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Actually, for performance reasons, you almost always want to put your script tags at the bottom of your page. Why? You want your page structure and your CSS to load first so that the user sees the page right away. Then you want all your behavior driven code to load last. YSlow is a good firefox extension that will show you a grade for performance. One of the items it grades you on is whether you have javascript at the bottom rather than the top.

blocks|key|1489453|text|在某些情况下，是的，如果脚本位于错误的位置，则脚本可能无法工作。一些JavaScript需要在特定的HTML元素之后执行，其他的需要在您希望脚本输出显示的位置，其他的应该在文档的头部。这真的取决于代码是如何编写的。如果您不确定，则应在window.load或DOMready：http://www.javascriptkit.com/dhtmltutors/domready.shtml上执行代码|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1489454|entityMap|0|LINK|mutability|MUTABLE|url|http://www.javascriptkit.com/dhtmltutors/domready.shtml^0|3U|1J|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

In some cases, yes the script may not work if its in the wrong location. Some JavaScript needs to be executed after a specific HTML element, others need to be exactly where you want your script output to show, others should be in the head of the document. It really depends on how the code is written. If you are not sure, you should execute your code on window.load or DOMready: <a href="http://www.javascriptkit.com/dhtmltutors/domready.shtml" rel="nofollow noreferrer">http://www.javascriptkit.com/dhtmltutors/domready.shtml</a>

I believe javascript can be anywhere (almost), but I almost always see it in between <code>&lt;head&gt;&lt;/head&gt;</code>. I am using jquery and wanted to know if it has to be in the head tags for some reason or if will break something if I move it. Thank you.

EDIT: Why is it almost always in the head tags?

Does javascript have to be in the head tags?

jQuery

我相信javascript可以在任何地方(几乎)出现，但我几乎总是在<head></head>之间看到它。我正在使用jquery，我想知道它是否出于某种原因必须在head标签中，或者如果我移动它是否会损坏某些东西。谢谢。编辑:为什么它几乎总是在head标签中？

问javascript必须在head标签中吗？
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问javascript必须在head标签中吗？
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