库定义

什么是 "库定义"？

¥What's a "Library Definition"?

大多数真正的 JavaScript 程序都依赖于第三方代码，而不仅仅是直接受项目控制的代码。这意味着使用 Flow 的项目可能需要引用没有类型信息或没有准确和/或精确类型信息的外部代码。为了解决这个问题，Flow 支持 "库定义"（又名 "库定义文件"）的概念。

¥Most real JavaScript programs depend on third-party code and not just code immediately under the control of the project. That means a project using Flow may need to reference outside code that either doesn't have type information or doesn't have accurate and/or precise type information. In order to handle this, Flow supports the concept of a "library definition" (a.k.a. "libdef").

libdef 是一个特殊文件，它向 Flow 通知你的应用使用的某些特定第三方模块或模块包的类型签名。如果你熟悉具有头文件的语言（例如 C++），你可以将 libdef 视为类似的概念。

¥A libdef is a special file that informs Flow about the type signature of some specific third-party module or package of modules that your application uses. If you're familiar with languages that have header files (like C++), you can think of libdefs as a similar concept.

这些特殊文件使用与普通 JS 代码相同的 .js 扩展名，但它们放置在项目根目录中名为 flow-typed 的目录中。放置在此目录中会告诉 Flow 将它们解释为 libdef，而不是普通的 JS 文件。

¥These special files use the same .js extension as normal JS code, but they are placed in a directory called flow-typed in the root directory of your project. Placement in this directory tells Flow to interpret them as libdefs rather than normal JS files.

注意：使用 libdefs 的 /flow-typed 目录是一种约定，它使 Flow 能够开箱即用，并鼓励使用 Flow 的项目之间的一致性，但也可以显式配置 Flow 以使用 .flowconfig 的 [libs] 部分 在其他地方查找 libdefs。

¥NOTE: Using the /flow-typed directory for libdefs is a convention that enables Flow to JustWork™ out of the box and encourages consistency across projects that use Flow, but it is also possible to explicitly configure Flow to look elsewhere for libdefs using the [libs] section of your .flowconfig.

你还可以了解 声明文件。

¥You can also learn about declaration files.

一般最佳实践

¥General Best Practices

尝试为你的项目使用的每个第三方库提供一个 libdef。

¥Try to provide a libdef for each third-party library your project uses.

如果你的项目使用没有类型信息的第三方库，Flow 会将其视为任何其他无类型依赖，并将其所有导出标记为 any。

¥If a third-party library that has no type information is used by your project, Flow will treat it like any other untyped dependency and mark all of its exports as any.

由于这种行为，最佳实践是为你使用的尽可能多的第三方库查找或编写 libdef。我们建议查看 flow-typed 工具和存储库 ，它可以帮助你快速查找并安装第三方依赖的预先存在的 libdef。

¥Because of this behavior, it is a best practice to find or write libdefs for as many of the third-party libraries that you use as you can. We recommend checking out the flow-typed tool and repository , which helps you quickly find and install pre-existing libdefs for your third-party dependencies.