Module Types

 

Importing and exporting types

It is often useful to share types in between modules (files). In Flow, you can export type aliases, interfaces, and classes from one file and import them in another.

exports.js

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// @flow
export default class Foo {};
export type MyObject = { /* ... */ };
export interface MyInterface { /* ... */ };

imports.js

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// @flow
import type Foo, {MyObject, MyInterface} from './exports';
Cannot resolve module `./exports`.

Don’t forget to mention @flow on top of file, otherwise flow won’t report errors.

Importing and exporting values

Flow also supports importing the type of values exported by other modules using typeof.

exports.js

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// @flow
const myNumber = 42;
export default myNumber;
export class MyClass {
  // ...
}

imports.js

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// @flow
import typeof myNumber from './exports';
import typeof {MyClass} from './exports';
Cannot resolve module `./exports`. Cannot resolve module `./exports`.

Just like other type imports, this code will be stripped away by a compiler and will not add a dependency on the other module.

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