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120 lines
3.1 KiB
Markdown
120 lines
3.1 KiB
Markdown
# Import and export modules
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## Concepts
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- [import](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import)
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allows you to include and use modules held elsewhere, on your local file
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system or remotely.
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- Imports are URLs or file system paths.
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- [export](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export)
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allows you to specify which parts of your module are accessible to users who
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import your module.
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## Overview
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Deno by default standardizes the way modules are imported in both JavaScript and
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TypeScript using the ECMAScript 6 `import/export` standard.
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It adopts browser-like module resolution, meaning that file names must be
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specified in full. You may not omit the file extension and there is no special
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handling of `index.js`.
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```js
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import { add, multiply } from "./arithmetic.ts";
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```
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Dependencies are also imported directly, there is no package management
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overhead. Local modules are imported in exactly the same way as remote modules.
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As the examples show below, the same functionality can be produced in the same
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way with local or remote modules.
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## Local Import
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In this example the `add` and `multiply` functions are imported from a local
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`arithmetic.ts` module.
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**Command:** `deno run local.ts`
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```ts
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/**
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* local.ts
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*/
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import { add, multiply } from "./arithmetic.ts";
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function totalCost(outbound: number, inbound: number, tax: number): number {
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return multiply(add(outbound, inbound), tax);
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}
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console.log(totalCost(19, 31, 1.2));
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console.log(totalCost(45, 27, 1.15));
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/**
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* Output
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*
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* 60
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* 82.8
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*/
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```
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## Remote Import
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In the local import example above an `add` and `multiply` method are imported
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from a locally stored arithmetic module. The same functionality can be created
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by importing `add` and `multiply` methods from a remote module too.
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In this case the Ramda module is referenced, including the version number. Also
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note a JavaScript module is imported directly into a TypeScript module, Deno has
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no problem handling this.
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**Command:** `deno run ./remote.ts`
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```ts
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/**
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* remote.ts
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*/
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import {
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add,
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multiply,
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} from "https://x.nest.land/ramda@0.27.0/source/index.js";
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function totalCost(outbound: number, inbound: number, tax: number): number {
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return multiply(add(outbound, inbound), tax);
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}
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console.log(totalCost(19, 31, 1.2));
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console.log(totalCost(45, 27, 1.15));
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/**
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* Output
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*
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* 60
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* 82.8
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*/
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```
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## Export
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In the local import example above the `add` and `multiply` functions are
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imported from a locally stored arithmetic module. To make this possible the
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functions stored in the arithmetic module must be exported.
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To do this just add the keyword `export` to the beginning of the function
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signature as is shown below.
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```ts
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/**
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* arithmetic.ts
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*/
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export function add(a: number, b: number): number {
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return a + b;
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}
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export function multiply(a: number, b: number): number {
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return a * b;
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}
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```
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All functions, classes, constants and variables which need to be accessible
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inside external modules must be exported. Either by pretending them with the
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`export` keyword or including them in an export statement at the bottom of the
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file.
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