https://github.com/jonaskuske/promise-aplus

🔮 An A+ compliant Promise implementation
https://github.com/jonaskuske/promise-aplus

Last synced: 11 months ago
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🔮 An A+ compliant Promise implementation

• Host: GitHub
• URL: https://github.com/jonaskuske/promise-aplus
• Owner: jonaskuske
• License: mit
• Created: 2022-11-23T23:38:09.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2022-11-25T02:14:08.000Z (over 3 years ago)
• Last Synced: 2025-03-29T23:17:53.759Z (about 1 year ago)
• Language: JavaScript
• Size: 1.13 MB
• Stars: 2
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# A+ compliant promise implementation



    



A Promise implementation that utilizes modern ES2022 features like private class fields and fully complies with the [Promises/A+ 1.1.0 specification](https://promisesaplus.com/). Requires a runtime with `queueMicrotask` like browsers or Node.

### Available functions

```js

// Create new Promise that immediately resolves

promise = Promise.resolve(valueOrThenable)

// Create new Promise that immediately rejects

promise = Promise.reject(reason)

// Create new Promise, must pass executor functiom

promise = new Promise((resolve, reject) => {})

// Return new Promises with resolve/reject handlers applied

promise.then(onResolve, onReject)

promise.catch(onReject)

```

### Example

```js

import { Promise } from "./promise.js"

function retryIfEmpty(fn, retry = 1, signal) {

	retry = Math.max(0, retry)

	const end = new (class extends Error {

		name = "RetryError"

		message = "maximum tries reached"

	})()

	return new Promise((resolve, reject) => {

		signal?.throwIfAborted()

		signal?.addEventListener("abort", reject)

		Promise.resolve(fn()).then((val) => {

			resolve(

				val ?? (retry > 0 ? retryIfEmpty(fn, --retry, signal) : Promise.reject(end)),

			)

		}, reject)

	})

}

retryIfEmpty(() => Math.random() > 0.5 || null, 2).catch((e) => {

	if (e.name !== "RetryError") throw e

	return false

})

```

### Verify

**`yarn test`**: Run A+ test suite against this Promise implementation

**`yarn test-builtin`**: Run A+ test suite against the native built-in `Promise`

**`yarn test-deferred`**: Run deferred tests and A+ test suite against `DeferredPromise`




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©️ 2022, Jonas Kuske