Javascript：使用setTimeout重试的函数 [英] Javascript: Function that retries with setTimeout

问题描述

我有一个函数 downloadItem ，由于网络原因可能会失败，我希望能够在实际拒绝该项目之前重试几次。重试需要超时，因为如果出现网络问题，立即重试是没有意义的。

I have a function downloadItem that may fail for network reasons, I want to be able to retry it a few times before actually rejecting that item. The retries need to be with a timeout since if there is a network issue there is no point in retrying immediately.

这是我到目前为止所做的：

Here is what I have so far:

function downloadItemWithRetryAndTimeout(url, retry, failedReason) {
    return new Promise(function(resolve, reject) {
        try {
            if (retry < 0 && failedReason != null) reject(failedReason);

            downloadItem(url);
            resolve();
        } catch (e) {
            setTimeout(function() {
                downloadItemWithRetryAndTimeout(url, retry - 1, e);
            }, 1000);
        }
    });
}

显然这会因为我打电话的第二个（和开启时间）而失败 downloadItemWithRetryAndTimeout 我没有按要求返回承诺。

Obviously this will fail since the second (and on) time I call downloadItemWithRetryAndTimeout I don't return a promise as required.

如何让它与第二个承诺正常工作？

How do I make it work correctly with that second promise?

PS因为代码在NodeJS中运行很重要。

P.S. incase it matters the code is running in NodeJS.

推荐答案

我有两个想法：

移动迭代函数downloadItemWithRetryAndTimeout的promise - 现在resolve（）将可用于所有迭代：

Move the promise out side of the iterated function downloadItemWithRetryAndTimeout - now resolve() will available to all iterations:

function downloadWrapper(url, retry) {
    return new Promise(function (resolve, reject) {
        function downloadItemWithRetryAndTimeout(url, retry, failedReason) {

            try {
                if (retry < 0 && failedReason != null)
                    reject(failedReason);

                downloadItem(url);
                resolve();
            } catch (e) {
                setTimeout(function () {
                    downloadItemWithRetryAndTimeout(url, retry - 1, e);
                }, 1000);
            }

        }

        downloadItemWithRetryAndTimeout(url, retry, null);
    });
}

此解决方案有效，但它违反了承诺链，这是一种反模式：
当每次迭代返回一个promise时，只需解析promise，然后使用.then解析之前的promise，依此类推：

This solution works, but it's an anti pattern as it breaks the promise chain: As each iteration returns a promise, just resolve the promise, and use .then to resolve the previous promise, and so on:

function downloadItemWithRetryAndTimeout(url, retry, failedReason) {
    return new Promise(function (resolve, reject) {
        try {
            if (retry < 0 && failedReason != null)
                reject(failedReason);

            downloadItem(url);
            resolve();
        } catch (e) {
            setTimeout(function () {
                downloadItemWithRetryAndTimeout(url, retry - 1, e).then(function () {
                    resolve();
                });
            }, 1000);
        }
    });
}

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