此为官方文档,因为墙的问题,记录下来:
Before spending the time to write your own libdef, we recommend that you look to see if there is already a libdef for the third-party code that you’re addressing. flow-typed
is a tool and repository for sharing common libdefs within the Flow community – so it’s a good way to knock out a good chunk of any public libdefs you might need for your project.
However sometimes there isn’t a pre-existing libdef or you have third-party code that isn’t public and/or you really just need to write a libdef yourself. To do this you’ll start by creating a .js
file for each libdef you’re going to write and put them in the /flow-typed
directory at the root of your project. In these libdef file(s) you’ll use a special set of Flow syntax (explained below) to describe the interfaces of the relevant third-party code.
Declaring A Global Function
To declare a global function that should be accessible throughout your project, use the declare function
syntax in a libdef file:
flow-typed/myLibDef.js
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This tells Flow that any code within the project can reference the foo
global function, and that the function takes one argument (a number
) and it returns a string
.
Declaring A Global Class
To declare a global class that should be accessible throughout your project, use the declare class
syntax in a libdef file:
flow-typed/myLibDef.js
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This tells Flow that any code within the project can reference the URL
global class. Note that this class definition does not have any implementation details – it exclusively defines the interface of the class.
Declaring A Global Variable
To declare a global variable that should be accessible throughout your project, use the declare var
syntax in a libdef file:
flow-typed/myLibDef.js
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This tells Flow that any code within the project can reference the PI
global variable – which, in this case, is a number
.
Declaring A Global Type
To declare a global type that should be accessible throughout your project, use the declare type
syntax in a libdef file:
flow-typed/myLibDef.js
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This tells Flow that any code within the project can reference the UserID
global type – which, in this case, is just an alias for number
.
Declaring A Module
Often, third-party code is organized in terms of modules rather than globals. To write a libdef that declares the presence of a module you’ll want to use the declare module
syntax:
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The name specified in quotes after declare module
can be any string, but it should correspond to the same string you’d use to require
or import
the third-party module into your project. For defining modules that are accessed via a relative require
/import
path, check out the docs on .js.flow
files.
Within the body of a declare module
block, you can specify the set of exports for that module. However, before we start talking about exports we have to talk about the two kinds of modules that Flow supports: CommonJS and ES modules.
Flow can handle both CommonJS and ES modules, but there are some relevant differences between the two that need to be considered when using declare module
.
Declaring An ES Module
ES modules have two kinds of exports: A named export and a default export. Flow supports the ability to declare either or both of these kinds of exports within a declare module
body as follows:
Named Exports
flow-typed/some-es-module.js
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Note that you can also declare other things inside the body of the declare module
, and those things will be scoped to the body of the declare module
– but they will not be exported from the module:
flow-typed/some-es-module.js
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Default Exports
flow-typed/some-es-module.js
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It is also possible to declare both named and default exports in the same declare module
body.
Declaring A CommonJS Module
CommonJS modules have a single value that is exported (the module.exports
value). To describe the type of this single value within a declare module
body, you’ll use the declare module.exports
syntax:
flow-typed/some-commonjs-module.js
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Note that you can also declare other things inside the body of the declare module
, and those things will be scoped to the body of the declare module
, but they will not be exported from the module:
flow-typed/some-commonjs-module.js
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NOTE: Because a given module cannot be both an ES module and a CommonJS module, it is an error to mix declare export [...]
with declare module.exports: ...
in the same declare module
body.