即使在'end'事件上指定return，NodeJS http.request也不返回数据 [英] NodeJS http.request not returning data even after specifying return on the 'end' event

问题描述

基本上我试图从网站上删除一些数据并在绑定到 http.request 的'end'事件的回调函数上执行DOM提取，删除和更新。

Basically I am trying to scrap some data from website and perform the DOM extraction, deletion and updation on a callback function binded to the 'end' event of http.request.

我已经从'end'事件回调中返回了数据但是我的路线中没有收到回调函数。我得到 undefined 那里。

I have returned the data from the 'end' event callback too but it is not receiving in my route callback function. I get undefined there.

下面是代码块：

var scraper = {
    extractEmail: function (directoryName) {
        var result = getDirectory(directoryName);
        if (result !== 404) {
            var protocol = result.https ? https : http;
            protocol.request({
                host: 'somevalue.net',
                method: "GET"
            }, function (res) {
                var data = '';
                res.on('data', function (chunk) {
                    data += chunk;
                });

                res.on('end', function () {
                    return data;
                });
            })
                .on('error', function (err) {
                    return err;
                })
                .end();
            //return data;
        }
        else {
            //return "Failed";
        }
    }
};

这是Routes.js函数：

And here is the Routes.js function:

app.get('/:directory', function (req, res) {
    var n = scraper.extractEmail(req.params.directory);
    console.log(n);
    res.send(n);
});

在这里我也没有得到 n 。

推荐答案

您无法从异步回调中返回值。嗯，你可以，但它很可能会被忽略，而且肯定不会做你想要的。

You cannot return a value from an asynchronous callback. Well, you can, but it most likely will get ignored and most certainly won't do what you want.

你甚至不能在那个地方回复承诺。您只能解决现在使用return语句的promise。您需要从main函数返回一个promise，然后在现在使用return的事件处理程序中解析或拒绝promise。

You cannot even return a promise in that place. You can only resolve a promise where you now use the return statements. You need to return a promise from the main function and then resolve or reject the promise in your event handlers where you use returns now.

有关详细信息，请参阅以下答案：

For more info see those answers:

• 返回Promise结果而不是Nodejs中的Promise


• 从函数块返回函数值


• jQuery：ajax调用成功后返回数据

• Return Promise result instead of Promise in Nodejs
• Return value in function from a promise block
• jQuery: Return data after ajax call success

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