为什么不再使用 X-UA-Compatible IE=Edge? [英] Why use X-UA-Compatible IE=Edge anymore?
问题描述
我最近参加了几门在线课程，但我仍然看到一些教师默认将以下元标记添加到他们的文档顶部:
这种想法似乎与 一样重要和有用.
为什么?
根据.
<块引用>自 2016 年 1 月 12 日起，只有适用于受支持操作系统的最新版本的 Internet Explorer 才能获得技术支持和安全更新.Internet Explorer 11 是 Internet Explorer 的最后一个版本，将继续在 Windows 7、Windows 8.1 和 Windows 10 上获得安全更新、兼容性修复和技术支持.>
IE11 是唯一的 官方支持的 IE 版本.
在 HTML 中包含 X-UA-Compatible 元标记的唯一原因是在 IE8、9 和 10 中为您的网站覆盖用户的兼容性视图"设置.几乎在所有情况下，用户都不会更改这些设置(为什么要更改?)，现在这些浏览器甚至不再受支持.
简而言之:这个标签已经过时了.
I've taken several online courses lately and I still see some instructors add the following meta tag to the top of their documents by default:
<meta http-equiv="X-UA-Compatible" content="IE=edge">
The thinking appears to be that this is just as important and useful as <meta charset="UTF-8">.
But why?
According to Microsoft's Modern.ie documentation it's "best practice" which "ensures Internet Explorer uses the latest engine". Ok, fair enough.
However, if you follow the flow diagram on MSDN it clearly shows that a document without X-UA-Compatible information is forwarded to the user's "Compatibility View" preferences, and if that's not set then just follow the !DOCTYPE declaration.
In other words, unless the user has some Compatibility View settings in place, IE will just follow your !DOCTYPE and use the latest standards mode of your browser for rendering anyway... No need for a X-UA-Compatible IE=Edge statement at all.
As MSDN says: "Use the HTML5 document type declaration to enable edge mode".
So in what circumstances is X-UA-Compatible IE=Edge needed?
As @David's answer points out, unless you're hosting a site in the "Local Intranet" zone, there is very little reason to include <meta http-equiv="X-UA-Compatible" content="IE=edge"> in your webpages, and (according to Microsoft's best practice recommendations) absolutely no reason to include it in the HTML. (You should place it in your server config or site headers -- not in the HTML itself.)
If you are considering using X-UA-Compatible anywhere in your project, you should remember that Compatibility View only affects IE8, 9 and 10. It was only introduced in IE8 and was disabled in IE11.
Also be aware that IE11 is the only officially supported version of IE at this time. All older versions should be considered insecure.
If that wasn't enough reason to convince you not to use it, consider that Microsoft state that IE8 and above already automatically render in Standards Mode when a <!DOCTYPE is present, making it even more pointless.
You can see for yourself the flow that IE takes to decide what document mode to use:
As you can see, if no X-UA-Compatible meta tag or HTTP header is present, it checks the user's "Compatibility View" settings. If the user doesn't have any for your website, IE then checks for the presence of a <!DOCTYPE declaration. If it finds one it automatically uses the latest Standards Mode (aka "EmulateIEx"). If it doesn't, it reverts to Quirks Mode.
Even more reasons why you shouldn't use the "X-UA-Compatible" meta tag from Microsoft themselves (emphasis mine):
When Internet Explorer encounters the X-UA-Compatible META tag it starts over using the designated version's engine. This is a performance hit because the browser must stop and restart analyzing the content.
In other words, It slows initial page render
The X-UA-Compatible directive is a tool to allow applications to work in the latest Internet Explorer version while updates are made to the application.
It was only ever designed for temporary use.
The best practice is an X-UA-Compatible HTTP Header. Adding the directive to the response header tells Internet Explorer what engine to use before parsing content begins. This must be configured in the web site's server.
In other words, there's better ways of implementing X-UA-Compatible if you absolutely need it.
Starting from 12 January 2016, only the most current version of Internet Explorer available for a supported operating system will receive technical supports and security updates. Internet Explorer 11 is the last version of Internet Explorer, and will continue to receive security updates, compatibility fixes and technical support on Windows 7, Windows 8.1 and Windows 10.
IE11 is the only officially supported version of IE.
The only reason to include the X-UA-Compatible meta tag in your HTML was to override a user's "Compatibility View" settings in IE8, 9 and 10 for your website. In almost every case the user will not have changed these settings (why would they?), and now those browsers are not even supported anymore.
In short: This tag has had its day.
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