我以前的工作代码在迭代的每个元素上都低效地调用了等待。我正在重构以使用 Promise.All。 但是,在执行进一步代码之前,我的代码不会等待 Promise.All 解决。
具体来说,purgeRequestPromises
行在初始 Promise.All
解析之前执行。我不确定这是为什么? retrieveSurrogateKey
是一个异步函数,因此它的返回行将包含在一个已解决的 promise 中。
try {
//retrieve surrogate key associated with each URL/file updated in push to S3
const surrogateKeyPromises = urlArray.map(url => this.retrieveSurrogateKey(url));
const surrogateKeyArray = await Promise.all(surrogateKeyPromises).catch(console.log);
//purge each surrogate key
const purgeRequestPromises = surrogateKeyArray.map(surrogateKey => this.requestPurgeOfSurrogateKey(surrogateKey));
await Promise.all(purgeRequestPromises);
// GET request the URLs to warm cache for our users
const warmCachePromises = urlArray.map(url => this.warmCache(url));
await Promise.all(warmCachePromises)
} catch (error) {
logger.save(`${'(prod)'.padEnd(15)}error in purge cache: ${error}`);
throw error
}
async retrieveSurrogateKey(url) {
try {
axios({
method: 'HEAD',
url: url,
headers: headers,
}).then(response => {
console.log("this is the response status: ", response.status)
if (response.status === 200) {
console.log("this is the surrogate key!! ", response.headers['surrogate-key'])
return response.headers['surrogate-key'];
}
});
} catch (error) {
logger.save(`${'(prod)'.padEnd(15)}error in retrieveSurrogateKey: ${error}`);
throw error
}
}
我知道 purgeRequestPromises 会提前执行,因为我收到错误,抱怨我在 HEAD 请求中将 Surrogate-Key 标头设置为 undefined
:
async requestPurgeOfSurrogateKey(surrogateKey) {
headers['Surrogate-Key'] = surrogateKey
try {
axios({
method: `POST`,
url: `https://api.fastly.com/service/${fastlyServiceId}/purge/${surrogateKey}`,
path: `/service/${fastlyServiceId}/purge${surrogateKey}`,
headers: headers,
})
.then(response => {
console.log("the status code for purging!! ", response.status)
if (response.status === 200) {
return true
}
});
} catch (error) {
logger.save(`${'(prod)'.padEnd(15)}error in requestPurgeOfSurrogateKey: ${error}`);
throw error;
}
}
答案 0 :(得分:3)
retrieveSurrogateKey
同步返回 undefined
:try
块中的值是一个 promise 并且不会同步抛出错误,因此永远不会执行 catch
子句并执行掉出底部,从函数体返回 undefined
。
您可以尝试以下操作:
function retrieveSurrogateKey(url) { // returns a promise
return axios({
// ^^^^^^
method: 'HEAD',
url: url,
headers: headers,
}).then(response => {
console.log("this is the response status: ", response.status)
if (response.status === 200) {
console.log("this is the surrogate key!! ", response.headers['surrogate-key'])
return response.headers['surrogate-key'];
}
}).catch(error => {
logger.save(`${'(prod)'.padEnd(15)}error in retrieveSurrogateKey: ${error}`);
throw error;
});
}
请注意,如果函数不使用 async
,则将返回承诺的函数声明为 await
是多余的。这一行还有一个次要问题:
const surrogateKeyArray = await Promise.all(surrogateKeyPromises).catch(console.log);
除非重新抛出错误,否则 catch
子句将履行承诺链。您可以(也许)省略 .catch
子句或将其重新编码为
.catch( err=> { console.log(err); throw err} );
答案 1 :(得分:0)
您不必从 async
中删除 retrieveSurrogateKey()
才能使其工作。事实上,如果你不这样做,它更具可读性。正如已经解释过的,问题在于 retrieveSurrogateKey()
返回的承诺没有跟随对 axios()
的调用返回的承诺的完成。你需要await
:
async retrieveSurrogateKey(url) {
try {
const response = await axios({
method: 'HEAD',
url,
headers,
});
console.log('this is the response status: ', response.status);
if (response.status === 200) {
const surrogateKey = response.headers['surrogate-key'];
console.log('this is the surrogate key!! ', surrogateKey);
return surrogateKey;
}
} catch (error) {
logger.save(`${'(prod)'.padEnd(15)}error in retrieveSurrogateKey: ${error}`);
throw error;
}
}
这保留了您当前拥有的相同逻辑,但您会注意到,当 response.status !== 200
时,您最终会得到 undefined
的已解决承诺,而不是被拒绝的承诺。您可能希望使用 validateStatus
来断言 200 的确切状态。默认情况下,axios 会解析状态 >= 200 和 < 300 的任何响应:
async retrieveSurrogateKey(url) {
try {
const response = await axios({
method: 'HEAD',
url,
headers,
validateStatus(status) {
return status === 200;
}
});
const surrogateKey = response.headers['surrogate-key'];
console.log('this is the surrogate key!! ', surrogateKey);
return surrogateKey;
} catch (error) {
logger.save(`${'(prod)'.padEnd(15)}error in retrieveSurrogateKey: ${error}`);
throw error;
}
}
这样,您总能得到一个代理键或被拒绝的承诺。