Javascript 在 Node 中处理嵌套异步等待调用的正确方法是什么？
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What is the correct way to handle nested async await calls in Node?
提问by user3162553
Trying to learn the async pattern in Javascript but it doesn't appear that it waits for the following line. In the following example, the collection is the request object and not the actual parsed body. Isn't awaitsupposed to wait for the request to finish?
尝试学习 Javascript 中的异步模式，但它似乎没有等待以下行。在以下示例中，集合是请求对象，而不是实际解析的正文。不await应该等待请求完成吗？
async function importUsers(endpoint) {
const options = {
data: search,
uri: endpointCollection,
headers,
}
try {
const collection = await browser.post(options, (err, res, body) => JSON.parse(body))
// collection is the request object instead of the result of the request
const users = await collection.data.forEach(item => parseUserProfile(item));
await users.forEach(user => saveUserInfo(user))
} catch(err) {
handleError(err)
}
}
async function parseUserProfile({ username, userid }) {
const url = userProfileString(username)
try {
const profile = await browser.get(url, headers, (err, res, body) => {
return { ... } // data from the body
})
} catch(err) {
handleError(err)
}
}
回答by Get Off My Lawn
Async/Await only works on functions that return (and resolve) a promise.
Async/Await 仅适用于返回（并解析）promise 的函数。
The following example will write to the console after 3 seconds, and then continue on.
以下示例将在 3 秒后写入控制台，然后继续。
// Tell the browser that this function is asynchronous
async function myFunc() {
// Await for the promise to resolve
await new Promise((resolve) => {
setTimeout(() => {
// Resolve the promise
resolve(console.log('hello'));
}, 3000);
});
// Once the promise gets resolved continue on
console.log('hi');
}
// Call the function
myFunc();Without async/await, the output would be as follows:
如果没有 async/await，输出将如下所示：
hi
hello
Here is an example without async/await:
这是一个没有 async/await 的例子：
// Tell the browser that this function is asynchronous
async function myFunc() {
// Skip await
new Promise((resolve) => {
setTimeout(() => {
// Resolve the promise
resolve(console.log('hello'));
}, 3000);
});
// Since await was not used, this will print first
console.log('hi');
}
// Call the function
myFunc();This would be because the hioutput would run and then after 3 seconds the timeout would run.
这是因为hi输出将运行，然后在 3 秒后超时将运行。
But with async/await, the output looks like this:
但是使用 async/await，输出如下所示：
hello
hi
This is because we await for the timeout then we run the hioutput.
这是因为我们等待超时然后运行hi输出。
回答by Sheng
awaitshould expect a promise, for a callback style async function, you can transform it like:
await应该期待一个承诺，对于回调样式的异步函数，您可以将其转换为：
new Promise((resolve, reject) => browser.post(options, (err, res, body) => resolve(JSON.parse(body))))
For an array, you need to map it to an array of promises, then use Promise.allto turn it to a 'promise of array', for example:
对于一个数组，你需要将它映射到一个promise数组，然后使用Promise.all将它变成一个'promise of array'，例如：
Promise.all(collection.data.map(item => parseUserProfile(item)))
