异步 simpleParser 返回空数组

Question

我想将我所有的 email 都放在一个列表中，但我的 promises 数组是空的。 我认为它与一些异步问题有关，但我不知道是什么问题。

var promises = [];

    const imap = new Imap(imapConfig);
    imap.once("ready", () => {
        imap.openBox("INBOX", false, () => {
            imap.search(["ALL", ["SINCE", new Date()]], (err, results) => {
                const f = imap.fetch(results, { bodies: "" });
                f.on("message", (msg) => {
                    msg.on("body", (stream) => {
                        simpleParser(stream, async (err, parsed) => {
                            const { from, subject, textAsHtml, text } = parsed;
                            promises.push(text);
                        });
                    });
                });
                f.once("end", () => {
                    console.log("Done fetching all messages!", promises);
                    imap.end();
                });
            });
        });
    });

    imap.connect();

    return await Promise.all(promises);

Answer 1

该问题是由于将回调与承诺混合而产生的。 回调不是同步的。 到目前为止，您的代码的工作方式是：

var promises = [];
const imap = new Imap(imapConfig);
imap.once("ready", () => {/*async code*/});
return await Promise.all(promises);

对于最简单的解决方案，您需要添加自定义Deferred object （您也可以使用jQuery.Deferred ）

function Deferred() {
    const self = this;
    self.promise = new Promise((resolve, reject) => {
        self.resolve = resolve;
        self.reject = reject;
    });
}

使用它，解决方案将是：

function Deferred() {
    const self = this;
    self.promise = new Promise((resolve, reject) => {
        self.resolve = resolve;
        self.reject = reject;
    });
}

var promises = [];
var defer = new Deferred();
const imap = new Imap(imapConfig);
imap.once("ready", () => {
    imap.openBox("INBOX", false, () => {
        imap.search(["ALL", ["SINCE", new Date()]], (err, results) => {
            const f = imap.fetch(results, { bodies: "" });
            f.on("message", (msg) => {
                msg.on("body", (stream) => {
                    simpleParser(stream, async (err, parsed) => {
                        const { from, subject, textAsHtml, text } = parsed;
                        promises.push(text);
                    });
                });
            });
            f.once("end", () => {
                console.log("Done fetching all messages!", promises);
                imap.end();
                defer.resolve();
            });
        });
    });
});

imap.connect();

await defer.promise;
return await Promise.all(promises);

其他可能的解决方案：promisify 回调https://zellwk.com/blog/converting-callbacks-to-promises/