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同步等待异步等待_异步/等待和承诺的解释

编程日记 2024-08-01 04:40:00

同步等待异步等待

The async / await operators make it easier to implement many async Promises. They also allow engineers to write clearer, more succinct, testable code.

async / await 运算符使实现许多异步Promises变得更加容易。它们还允许工程师编写更清晰，更简洁，可测试的代码。

To understand this subject, you should have a solid understanding of how Promises work.

要理解此主题，您应该对Promises的工作方式有扎实的了解。

基本语法 (Basic Syntax)

function slowlyResolvedPromiseFunc(string) { return new Promise(resolve => {setTimeout(() => {resolve(string);}, 5000);});
}async function doIt() {const myPromise = await slowlyResolvedPromiseFunc("foo");console.log(myPromise); // "foo"
}doIt();

There are a few things to note:

有几件事要注意：

The function that encompasses the await declaration must include the async operator. This will tell the JS interpreter that it must wait until the Promise is resolved or rejected.
包含await声明的函数必须包含async运算符。这将告诉JS解释器，它必须等待直到Promise被解决或拒绝为止。
The await operator must be inline, during the const declaration.
在const声明期间， await操作符必须是内联的。
This works for reject as well as resolve.
这既适用于reject ，也适用于resolve 。

嵌套的承诺与`Async` / `Await` (Nested Promises vs. `Async` / `Await`)

Implementing a single Promise is pretty straightforward. In contrast, Chained Promises or the creation of a dependency pattern may produce “spaghetti code”.

实现一个Promise非常简单。相反，链式承诺或依赖模式的创建可能会产生“意大利面条代码”。

The following examples assume that the request-promise library is available as rp.

以下示例假定request-promise库可以作为rp 。

链接/嵌套的承诺 (Chained/Nested Promises)

// First Promise
const fooPromise = rp("http://domain.com/foo");fooPromise.then(resultFoo => {// Must wait for "foo" to resolveconsole.log(resultFoo);const barPromise = rp("http://domain.com/bar");const bazPromise = rp("http://domain.com/baz");return Promise.all([barPromise, bazPromise]);
}).then(resultArr => {// Handle "bar" and "baz" resolutions hereconsole.log(resultArr[0]);console.log(resultArr[1]);
});

`async` `await`承诺 (`async` and `await` Promises)

// Wrap everything in an async function
async function doItAll() {// Grab data from "foo" endpoint, but wait for resolutionconsole.log(await rp("http://domain.com/foo"));// Concurrently kick off the next two async calls,// don't wait for "bar" to kick off "baz"const barPromise = rp("http://domain.com/bar");const bazPromise = rp("http://domain.com/baz");// After both are concurrently kicked off, wait for bothconst barResponse = await barPromise;const bazResponse = await bazPromise;console.log(barResponse);console.log(bazResponse);
}// Finally, invoke the async function
doItAll().then(() => console.log('Done!'));

The advantages of using async and await should be clear. This code is more readable, modular, and testable.

使用async和await的优势应该很明显。此代码更具可读性，模块化和可测试性。

It’s fair to note that even though there is an added sense of concurrency, the underlying computational process is the same as the previous example.

可以公平地注意到，即使增加了并发感，底层的计算过程也与前面的示例相同。

处理错误/拒绝 (Handling Errors / Rejection)

A basic try-catch block handles a rejected Promise.

基本的try-catch块可处理被拒绝的Promise。

async function errorExample() {try {const rejectedPromise = await Promise.reject("Oh-oh!");} catch (error) {console.log(error); // "Uh-oh!"}
}errorExample();

翻译自: https://www.freecodecamp.org/news/async-await-and-promises/

同步等待异步等待

https://www.dkcj.cn/info/12303.html

同步等待异步等待_异步/等待和承诺的解释

基本语法 (Basic Syntax)

嵌套的承诺与`Async` / `Await` (Nested Promises vs. `Async` / `Await`)

链接/嵌套的承诺 (Chained/Nested Promises)

`async` `await`承诺 (`async` and `await` Promises)

处理错误/拒绝 (Handling Errors / Rejection)

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基本语法 (Basic Syntax)

嵌套的承诺与Async / Await (Nested Promises vs. Async / Await)

链接/嵌套的承诺 (Chained/Nested Promises)

async await承诺 (async and await Promises)

处理错误/拒绝 (Handling Errors / Rejection)

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嵌套的承诺与`Async` / `Await` (Nested Promises vs. `Async` / `Await`)

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