关于前端:ES6中的-asyncawait-是什么呢

async/await 是什么？

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