Does javascript have to be in the head tags?
Question
I believe javascript can be anywhere (almost), but I almost always see it in between <head></head> . 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?
11 answers
solution1
45 2009-07-31 15:46:56
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 http://developer.yahoo.com/performance/rules.html#js_bottom .
solution2
38 ACCPTED 2009-07-31 15:46:15
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 $(document).ready(...) 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 head tag mostly out of tradition.
solution3
16 2009-07-31 15:46:37
Basically, browsers stop rendering page until .js files are completely downloaded and processed. Since they render page progressively as HTML arrives, the later .js files are referenced, the better user experience will be.
So the trick is to include only absolutely crucial scripts in the head , and load remaining ones towards the end of the page.
solution4
9 2009-07-31 15:46:25
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.
solution5
9 2016-11-10 21:31:07
JS changes so quickly these days with new frameworks coming out every week and each one claims to be "the bees knees" by its advocates.
Gumbo is right to say a script tag can be referenced anywhere that supports an inline element, but the choice to load an external JS file or include JS code within a tag is a decision made individually on a case-by-case basis.
Yes, the browser will stop to load JS when it is parsed and therefore, you need to consider how this will affect page load speed and functionality.
As of mid 2015 (the popular answer was in July 2009), giving mobile priority to page load speed requires a two request limit to the mobile / cell mast, which under 3G gives you a 28k (2x 14kb(yes)) payload. You need to consider 'paint to screen' (as Google names it) of 28k. This should provide the user with enough page content / interactivity to ensure that they're on the right page or right track. Jquery minified is currently 87.6lkb, so that "just ain't gonna cut the mustard!"
This is why most mobile pages sit for a couple of seconds before loading anything, even on 4G! Don't allow that. Page speed is king and users hit their back button before your JQuery file loads. Under 3G+, a 28k payload will load in < 1sec, so there is no reason why your page shouldn't start loading in that time. Next time you click a link on your phone, watch the loading bar sit and wait while it goes through all the tags on the next page!
Do not structure your page based on 7-year-old posts on SO (even if it's not wrong, just outdated). Decide where each piece of code is needed and make sure a user can use the most important aspects of a page before you try to load 6 JS frameworks that implement extravagant visual features and extensive data binding for your page.
BTW, Google prefers you push JS to the bottom because Google analytics code needs to be the very last thing to load.
Think before you code!
solution6
5 2009-07-31 15:49:08
No. SCRIPT is not only categorized as head.misc element but also as special element and thus everywhere allowed where inline elements are allowed. So you can put a SCRIPT wherever inline elements are allowed:
<p>foo <script>document.write("bar")</script></p>
In fact, some recommend to put SCRIPT elements at the end of the BODY just before the closing tag so that the whole document is parsed before the JavaScript is loaded. That is to prevent JavaScript from blocking parallel downloads.
solution7
2 2009-07-31 15:47:07
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.
solution8
2 2009-07-31 15:49:37
请注意您可能具有的对延迟的不良影响，具体取决于用户的浏览器以及您将Javascript放在页面中的确切位置 - 请参阅Steve Souders所说的所有内容，包括他斯坦福大学讲座的视频，并且他的工作成果留在了例如这里 （尽可能地将脚本放在页面底部等等）。
solution9
1 2009-07-31 15:46:46
Because you don't want JavaScript mixed with HTML - content with behaviour. Preferably you want it in a separate file.
Having JS elsewhere has advantages and disadventages - it will be executed at different time, for instance, and you can write to the document from javascript located in the body.
solution10
0 2009-07-31 15:46:42
It can go in the head or body tag. Just keep in mind that it will execute whenever is read and not necessarily when the document is finished loading. Take a look here .
solution11
0 2009-07-31 15:49:54
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: http://www.javascriptkit.com/dhtmltutors/domready.shtml
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