javascript - setInterval和promises产生PromiseRejectionHandledWarning

我有一个应用程序，在其中我必须不断在后台运行一些异步代码。我对应用程序进行了最小模拟。

let promise_chain = Promise.resolve();
let rejected_promise_count = 0;

const interval_id = setInterval(
    // Do some important polling. I will just always reject to demonstrate the problem.
    () => {
        promise_chain = promise_chain.then(() => {
            rejected_promise_count += 1;
            return Promise.reject();
        })
    },
    10
);

// Set timeout simulates the program being done.
setTimeout(
    () => {
        clearInterval(interval_id);
        promise_chain
            .then(() => end("Resolved! :D"))
            .catch(() => end("Rejected! D:"));
    },
    1000
);

function end(message) {
    console.log(message);
    console.log(`Amount of rejected promises created: `, rejected_promise_count);
}

这给出了很长的 list :

(node:29217) UnhandledPromiseRejectionWarning: undefined
(node:29217) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:29217) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:29217) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 2)
(node:29217) UnhandledPromiseRejectionWarning: undefined
(node:29217) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 3)
(node:29217) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 3)
(node:29217) UnhandledPromiseRejectionWarning: undefined
(node:29217) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 4)
(node:29217) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 4)

最终由这些结束:

(node:29217) UnhandledPromiseRejectionWarning: undefined
(node:29217) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 87)
(node:29217) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 87)
(node:29217) UnhandledPromiseRejectionWarning: undefined
(node:29217) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 88)
Rejected! D:
Amount of rejected promises created:  1
(node:30920) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 89)

我不太确定为什么节点不希望我异步处理这些，但是考虑到它以一定间隔运行，我真的别无选择。

如何摆脱无尽的警告列表，更重要的是，如何确保将来节点不会终止此过程，因为它认为我没有处理拒绝请求？

最佳答案

这取决于您要执行的操作，正确的处理方式如下所示:

const interval_id = setInterval(
    () => {
        promise_chain = promise_chain.then(() => {
            rejected_promise_count += 1;
            return Promise.reject();
        });
        //ignore error here, you catch it in the setTimeout
        promise_chain.catch(ignore=>ignore);
    },
    10
);

将会输出:

Rejected! D:
Amount of rejected promises created:  1

这是因为您第一次拒绝，所以链断了，其他所有then均未执行。

如果您想继续执行并想知道通过和失败的次数，可以执行以下操作:

//using actual results
let results = [];
//special Fail value to indicate rejected promise
let Fail = function(reason){this.reason=reason;};
let isFail = object=>(object&&object.constructor===Fail);
let isNotFail = object=>!isFail(object);

let promise_chain;
let somePromise = ()=>Promise.reject(new Error("Some reason"));

const interval_id = setInterval(
    () => {
        promise_chain = (promise_chain||somePromise())
        .then(
          result => {
            results.push(result);
            return somePromise();
          }
        )
        .catch(//catch the rejection and return a Fail type value
          error=>new Fail(error)
        );
},
    10
);

// Set timeout simulates the program being done.
setTimeout(
    () => {
        clearInterval(interval_id);
        promise_chain
        .then(
          result => {
            //add the last result to results
            results.push(result);
            console.log(
              "rejected promises:",
              results.filter(isFail).length
              //you can get the errors like so:
              //results.filter(isFail).map(fail=>fail.reason)
            );
            console.log(
              "resolved promises:",
              results.filter(isNotFail).length
              //results.filter(isNotFail) is an array of resolved values
            )
          }
        );
            //this will never reject because we catch rejected promises
            //  and add fail types to results
            // .catch(() => end("Rejected! D:"));
    },
    1000
);

关于javascript - setInterval和promises产生PromiseRejectionHandledWarning，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/49702054/