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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32
｜
第
4
章
何从
4.0.0
开始的
Express
版本都可以。因此，
4.0.1
和
4.9.9
都没问题，
3.4.7
则不行，
5.0.0
也不行。执行
npm install
时安装的是指定依赖版本，一般比较保险。但这样的结果是，
如果想升级到更新的版本，就必须编辑文件并指定这个新版本。通常来说这是好事，因为
避免了在你不知道的情况下，依赖发生了变更而破坏项目。
npm
中的版本号是由一个叫
semver
（表示
semantic
versioning
）的组件来解析的。如果想了解更多有关
npm
中版本的
信息，请查看“语义版本规范”。
“语义版本规范”规定采用语义版本的软件必须声明一个“公开
API
”。我总
觉得这个规定令人困惑，它其实想表达：一定会有人关心如何跟你的软件实
现对接。如果从广义角度考虑，它可以解释成任何东西。因此不要理会规范
的这个部分，重在语义版本的格式。
既然
package.json
文件已经列出了所有的依赖，那么
node_modules
目录实际上只是它的派
生物。也就是说，即使你删除了
node_modules
，要让项目再次正常运行
，需要做的也只
是运行
npm install
，这样就会重新创建这个目录，把运行项目所有必需的依赖都放进去。
正因如此，我推荐把
node_modules
加入
.gitignore
文件，但不包含进版本控制里。不过，
有些人觉得版本库应该包含任何运行项目所必需的东西，所以把
node_modules
包含进了版
本控制里。但我觉得这是版本库的“噪声”，宁愿不要它。
npm
版本
5
会创建一个额外的文件 ...
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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.