在可通过mergeMap传递的RxJ中继续发生错误
我正在使用RxJs管道和mergeMap运算符进行一些并行HTTP获取。
在第一个请求失败时(假设/ urlnotexists抛出404错误),它将停止所有其他请求。
我希望它继续查询所有剩余的URL,而不必为此失败的请求调用所有剩余的mergeMap。
我曾尝试将throwError和RxJs的catchError一起玩,但没有成功。
index.js
const { from } = require('rxjs');
const { mergeMap, scan } = require('rxjs/operators');
const request = {
get: url => {
return new Promise((resolve, reject) => {
setTimeout(() => {
if (url === '/urlnotexists') { return reject(new Error(url)); }
return resolve(url);
}, 1000);
});
}
};
(async function() {
await from([
'/urlexists',
'/urlnotexists',
'/urlexists2',
'/urlexists3',
])
.pipe(
mergeMap(async url => {
try {
console.log('mergeMap 1:', url);
const val = await request.get(url);
return val;
} catch(err) {
console.log('err:', err.message);
// a throw here prevent all remaining request.get() to be tried
}
}),
mergeMap(async val => {
// should not pass here if previous request.get() failed
console.log('mergeMap 2:', val);
return val;
}),
scan((acc, val) => {
// should not pass here if previous request.get() failed
acc.push(val);
return acc;
}, []),
)
.toPromise()
.then(merged => {
// should have merged /urlexists, /urlexists2 and /urlexists3
// even if /urlnotexists failed
console.log('merged:', merged);
})
.catch(err => {
console.log('catched err:', err);
});
})();
$ node index.js
mergeMap 1: /urlexists
mergeMap 1: /urlnotexists
mergeMap 1: /urlexists2
mergeMap 1: /urlexists3
err: /urlnotexists
mergeMap 2: /urlexists
mergeMap 2: undefined <- I didn't wanted this mergeMap to have been called
mergeMap 2: /urlexists2
mergeMap 2: /urlexists3
merged: [ '/urlexists', undefined, '/urlexists2', '/urlexists3' ]
我希望发出并发的GET请求,并最后在一个对象中减小它们各自的值。
但是如果发生某些错误,我希望他们不要中断我的管道,而要记录它们。
任何建议?
回答如下:如果您愿意放弃RXJS并仅使用async / await解决,则非常简单:
const urls = ['/urlexists', '/urlnotexists', '/urlexists2', '/urlexists3']
const promises = urls.map(url => request(url)
const resolved = await Promise.allSettled(promises)
// print out errors
resolved.forEach((r, i) => {
if (r.status === "rejected') {
console.log(`${urls[i]} failed: ${r.reason})
}
})
// get the success results
const merged = resolved.filter(r => r.status === "resolved").map(r => r.value)
console.log('merged', merged)
此方法使用Promise.allSettled提出的辅助方法。如果您的环境没有此方法,则可以按照this answer中所示的方法来实现。