JS 异步：Event-Loop+async/await

The await using declaration declares block-scoped local variables that are asynchronously disposed. Like const, variables declared with await using must be initialized and cannot be reassigned. The variable's value must be either null, undefined, or an object with a [Symbol.asyncDispose]() or [Symbol.dispose]() method. When the variable goes out of scope, the [Symbol.asyncDispose]() or [Symbol.dispose]() method of the object is called and awaited, to ensure that resources are freed.

js的执行机制是单线程 js的任务：同步任务和异步任务 异步任务： 宏任务：setTimeout setInterval（时间到了执行） event（click）事件触发 ajax 后台响应200微任务：promise

The await operator is used to wait for a Promise and get its fulfillment value. It can only be used inside an async function or at the top level of a module.

在前端编程中，经常会遇到异步处理，今天小编为大家简单讲解JS中异步中很著名的async/await，结合之前讲的Promise,相信大家读完这篇文章后会对JS中的异步操作有更深的理解。 什么是异步操作？ 在文章开始之前，先为不明白什么是异步操作的同学说一下什么是异步，简单的讲异步代码的执行，不会阻塞

Every medium or large game should compile asm.js code as part of an async script to give the browser the maximum flexibility to optimize the compilation process. In Gecko, async compilation allows the JavaScript engine to compile the asm.js off the main thread when the game is loading and cache the generated machine code so that the game doesn't need to be compiled on subsequent loads (starting in Firefox 28). To see the difference, toggle javascript.options.parallel_parsing in about:config.

参考链接 JavaScript是一个单线程的编程语言，这意味着它在同一个事件内只能做一件事 好处：你不必考虑并发、多线程的问题，这会让代码更加简洁 坏处：你在进行一些耗时长的操作（读取文件、网络通讯等）时，会阻塞整个程序 为了不引入多线程的概念，同时又能提高程序的效率，JS引入了异步的概念，具体如下

The for await...of statement creates a loop iterating over async iterable objects as well as sync iterables. This statement can only be used in contexts where await can be used, which includes inside an async function body and in a module.

文章开始我想请问大家，什么是异步？为什么需要异步？我想很多人的回答会是setTimeout，Promise，async await等等； 但是其实异步是一种概念，setTimeout，Promise，async await只是执行异步的方法； 我们都知道JS是单线程语言，也就是说我们在JS代码中输入

The JavaScript exception "await is only valid in async functions, async generators and modules" occurs when an await expression is used outside of async functions or modules or other async contexts.

Node.js is a JavaScript-based platform for server-side and networking applications.