Async on Commentary of Takao

JavaScript 非同步/等待應避免的模式

Sat, 15 Feb 2025 00:00:00 +0900

介紹

自從 ES2017 中引入 async/await 以來，編寫非同步 JavaScript 變得更加直觀。它允許開發人員以看起來同步的結構表達非同步邏輯，與嵌套的 Promise 鏈 (.then().catch()) 相比，大大提高了程式碼庫的可讀性。

JavaScript 事件循環深入探討：微任務、巨集任務及其他

Mon, 19 Feb 2024 00:00:00 +0900

JavaScript 事件循環是該語言中最重要但又被誤解的概念之一。儘管 JavaScript 是單線程的，但它的事件循環通過複雜的隊列系統實現了非阻塞並發。本文建構了 JavaScript 如何處理非同步執行的完整心智模型，從呼叫堆疊到微任務佇列以及其間的所有內容。

進階 JavaScript Promise Patterns: Async Control 流程 Mastery

Tue, 05 Dec 2023 00:00:00 +0900

Promises are fundamental to modern JavaScript, but mastering asynchronous control flow requires going beyond basic .then() chains. This article explores advanced Promise patterns that intermediate to senior developers need for production applications, from concurrency control to error handling and cancellation.

The Promise Landscape Beyond Basics

JavaScript provides four static methods on Promise for composing async operations, each suited to different scenarios:

Method	Resolves When	Rejects When	Use Case
`Promise.all`	All promises resolve	Any promise rejects	Parallel API calls, all required
`Promise.allSettled`	All promises settle	Never	Mixed results, log all outcomes
`Promise.race`	First promise settles	First promise rejects	Timeout race conditions
`Promise.any`	First promise resolves	All promises reject	First-successful-response pattern

const results = await Promise.allSettled([
 fetch("/api/users").then(r => r.json()),
 fetch("/api/posts").then(r => r.json()),
 fetch("/api/comments").then(r => r.json()),
]);
const successful = results.filter(r => r.status === "fulfilled").map(r => r.value);

Promise.allSettled is particularly useful when you need to process partial results even if some operations fail, such as batch data synchronization where individual record failures should not abort the entire batch.