关于前端:ES6中的-asyncawait-是什么呢

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async 函数，就是 Generator 函数的语法糖，它建设在 Promises 上，并且与所有现有的基于 Promise 的 API 兼容。

1、Async — 申明一个异步函数 (async function someName(){...} )

主动将惯例函数转换成 Promise，返回值也是一个Promise 对象
只有 async 函数外部的异步操作执行完，才会执行 then 办法指定的回调函数
异步函数外部能够应用 await

2、Await — 暂停异步的性能执行 (var result = await someAsyncCall() ) ????

搁置在 Promise 调用之前，await强制其余代码期待，直到 Promise 实现并返回后果
只能与 Promise 一起应用，不实用与回调
只能在 async 函数外部应用

What are the `async` and `await` ?

The async function, it’s a syntactic sugar of Geneartor function, it is built on Promise, and is compatible with all existing Promise-based API.

1、The async — declare a async function (async function someName(){...} )

Automatically convert regular functions to Promise, and the return value is also a Promise object.
Only after asynchronous operation inside async function is executed, then execute the callback function specified by then method.
we can use await inseide asynchronous function

2、The await — Paused the asnychronous function execution (var result = await someAsyncCall() )

Placed before the Promise Call, the await forced other codes to wait until the Promise completes and return the result.
Can only be used with Promise toghter, it’s not suitable for callback
Can only be used inside async function

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