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feat(example-context): add an example to demonstrate ValueOrPromise
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| @@ -0,0 +1,104 @@ | ||
| // Copyright IBM Corp. 2019. All Rights Reserved. | ||
| // Node module: @loopback/example-context | ||
| // This file is licensed under the MIT License. | ||
| // License text available at https://opensource.org/licenses/MIT | ||
|
|
||
| import { | ||
| Context, | ||
| ContextView, | ||
| filterByTag, | ||
| isPromiseLike, | ||
| resolveList, | ||
| resolveMap, | ||
| transformValueOrPromise, | ||
| ValueOrPromise, | ||
| } from '@loopback/context'; | ||
|
|
||
| /** | ||
| * A greeter | ||
| */ | ||
| interface Greeter { | ||
| language: string; | ||
| /** | ||
| * Greet in the given language | ||
| * @param name - Name | ||
| * @returns A message or a promise of a message | ||
| */ | ||
| greet(name: string): ValueOrPromise<string>; | ||
| } | ||
|
|
||
| class ChineseGreeter implements Greeter { | ||
| language = 'zh'; | ||
| greet(name: string) { | ||
| return `[value] 你好，${name}！`; | ||
| } | ||
| } | ||
|
|
||
| class EnglishGreeter implements Greeter { | ||
| language = 'en'; | ||
| greet(name: string) { | ||
| return `[value] Hello, ${name}!`; | ||
| } | ||
| } | ||
|
|
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| class AsyncChineseGreeter implements Greeter { | ||
| language = 'zh'; | ||
| greet(name: string) { | ||
| return new Promise<string>(resolve => | ||
| setImmediate(() => { | ||
| resolve(`[promise] 你好，${name}！`); | ||
| }), | ||
| ); | ||
| } | ||
| } | ||
|
|
||
| export async function main() { | ||
| const ctx = new Context('app'); | ||
|
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| // Add EnglishGreeter for now | ||
| ctx | ||
| .bind('greeters.EnglishGreeter') | ||
| .toClass(EnglishGreeter) | ||
| .tag('greeter'); | ||
|
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||
| // Add ChineseGreeter | ||
| ctx | ||
| .bind('greeters.ChineseGreeter') | ||
| .toClass(ChineseGreeter) | ||
| .tag('greeter'); | ||
|
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||
| const greetersView = ctx.createView<Greeter>(filterByTag('greeter')); | ||
| await greetFromAll(greetersView); | ||
|
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| // Replace ChineseGreeter with AsyncChineseGreeter | ||
| ctx | ||
| .bind('greeters.ChineseGreeter') | ||
| .toClass(AsyncChineseGreeter) | ||
| .tag('greeter'); | ||
|
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| await greetFromAll(greetersView); | ||
| } | ||
|
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| async function greetFromAll(greetersView: ContextView<Greeter>) { | ||
| const greeters = await greetersView.values(); | ||
| const greetings = resolveList(greeters, greeter => { | ||
| return greeter.greet('John'); | ||
| }); | ||
| if (isPromiseLike(greetings)) { | ||
| console.log('async:', await greetings); | ||
| } else { | ||
| console.log('sync:', greetings); | ||
| } | ||
| const greeterMap: { | ||
| [language: string]: Greeter; | ||
| } = {}; | ||
| greeters.filter(greeter => (greeterMap[greeter.language] = greeter)); | ||
| const greetingsByLanguage = resolveMap(greeterMap, greeter => | ||
| greeter.greet('Jane'), | ||
| ); | ||
|
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| await transformValueOrPromise(greetingsByLanguage, console.log); | ||
| } | ||
|
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| // tslint:disable-next-line:no-floating-promises | ||
| if (require.main === module) main(); |