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Import-export.md

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Importing and Exporting

Build modules are separate logical units that can export values. Build projects can import values from one or more build modules. Only values with 'public' visibility can be exported/imported.

Import

There are two ways to import values from a module:

  • in a declaration (import { X } from "MyModule"), and
  • within an expression (importFrom("MyModule").X).

The import declaration

Values may be imported from one or more modules at the top of a project definition. This is recommended when the imported value is used multiple times in the same project.

Standard import declaration

import * as Compression from "compression";
const zipArchive = Compression.Zip.pack([ f`file.txt` ]]);

Selective import declaration

import {Zip} from "compression";
const zipArchive = Zip.pack([ f`file.txt` ]);

Multiple selective import declaration

import {Zip, Gzip} from "compression";
const zipArchive = Zip.pack([ f`file.txt` ]);
const gzipArchive = Gzip.pack([ f`file.txt` ]);

Aliased selective import declaration

import {Zip as FastZip} from "compression";
const zipArchive = FastZip.pack([ f`file.txt` ]);

Aliased multiple selective import declaration

import {Zip as FastZip, GZip as GZ} from "compression";
const zipArchive = FastZip.pack([ f`file.txt` ]);
const gzip = GZ.pack([ f`file.txt` ]);

The importFrom expression

Elements from other modules may be imported within an expression using the importFrom function. This function takes the module's name (as a string value) to import and returns an object with all values exported by the selected module.

const zipArchive = importFrom("compression").Zip.pack([ f`file.txt` ]);

Note: Consider using a single import declaration at the file's top if you find yourself overusing importFrom with the same module in a single file.

Export

Declarations in a build project file are not visible to other projects unless they are explicitly exported with an export declaration. The declaration must also be marked as public with the @@public decorator to be visible to other modules.

Re-export a whole module

export * from "compression";

Selective re-export

export { Zip } from "compression";

Multiple selective re-export

export { Zip, Gzip } from "compression";

Aliased selective re-export

export { Zip as FastZip } from "compression";

Aliased multiple selective re-export

export { Zip as FastZip, Gzip as GZ } from "compression";

Exporting values

export const myValue = 42;

const myObject = { "foo": "bar" };
export { myObject };

Exporting imported values

import * as Compression from "compression";
import { Zip, Gzip as GZ } from "compression";

export { Compression, Zip, GZ as MyGZ };
export const gzipArchive = GZ.pack([ f`file.txt` ]);