June 2021
Intermediate to advanced
290 pages
9h 21m
Chinese
Content preview from Node与Express开发（第2版）
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192
｜
第
17
章
17.5
变更静态内容
缓存显著提升了网站的性能，但也有不利的一面，尤其是当你修改了某些静态资源时，在
浏览器缓存的版本过期之前，客户端可能看不到修改。谷歌推荐至少缓存一个月，缓存一
年则更好。假设有一个用户每天都在同一个浏览器上使用你的网站，那么他得整整一年才
能看到更新。
这种情形显然不是我们所希望的，而且你也不能逐一通知你的用户去清理缓存。解决方案
是使用
缓存破坏
。缓存破坏这项技术可以控制用户的浏览器何时重新下载某个资源。通常
缓存破坏是在资源名上带上一个版本号（
main.2.css
或
main.css?version=2
）
，或者带上某种
散列（
main.e16b7e149dccfcc399
e025e0c454bf77.css
）。不管是哪一种做法，变更这个资源时
资源名也会随之改变，而浏览器便知道了需要去下载它。
对多媒体资源也可以这样处理。不妨拿
logo
（
/static/img/mea
dowlark_logo.png
）做例子。
为了最大化性能，我们把它托管在
CDN
上
，指定一年后过期，之后如果修改这个
logo
，
那么用户在满一年之前可能都不会看到变更的
logo
。然而
，如果把它重命名为
static/img/
meadowlark_logo-1.png
（并且在
HTML
中体现出这个文件名修改）
，浏览器就只能下载它，
因为它看起来是一个新的资源。
如果使用一个单页应用的框架，类似
create-react-app
这样的工具就会提供一个构建步
骤，用以创建适合生产的资源包文件，并且会在这些资源包的文件名上追加一个散列。 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.