javascript - 退出一系列嵌套回调

Question

在下面的代码中，当从 deleteUser 的回调函数返回 err 变量时，我想将错误插入数据库并结束 HTTP 请求(并且这个整个代码块)，并return res.send(500)。

相反，即使 HTTP 请求已经结束，代码也会继续运行并调用 db.destroy。帖子底部的日志证明了这一点。

// DELETE
app.del('/api/users', function(req, res) {
    var id = req.query.id;

    // get latest copy of database entry first, in case we need to save error message
    db.get(id, {revs_info: true}, function(err, doc) {
        if (err) {
            console.error('Unable to find document', id, 'due to:', err);
            return res.send(500);
        } else {
            // issue delete request first, if fails save error message
            deleteUser(doc.EmailAddress, function(err) {
                if (err) {
                    // update database with error message (if there's already a message, append)
                    doc.Notes = (doc.Notes === '') ? err : err + " " + doc.Notes;

                    db.insert(doc, function(err, document) {
                        if(err) {
                            console.error('Deleting a user failed (1) and updating database with error status failed (2) as well. 1:', doc.Notes, '2:', err);
                            return res.send(500);
                        } else {
                            console.error('Deleting a user failed (with the following) and the error has been stored in the database:', doc.Notes);
                            return res.send(500);
                        }
                    });
                }

                // proceed to delete from database as well
                db.destroy(doc._id, doc._rev, function (err, body) {
                    if(err) {
                        console.error('Error deleting document', doc._id, 'with:', err);
                        return res.send(500);
                    } else {
                        if (doc._revs_info) delete doc._revs_info;
                        console.log('Succesfully deleted user from system and our database:', doc);
                        return res.send(200);
                    }
                });
            });
        }
    });
});

我认为发生这种情况是因为我的 return 语句仅结束 db.insert 函数。

Node 中是否有解决此问题的通用设计模式？

我是否应该在 db.insert 声明之后、if (err) { 代码块结束之前添加另一个 return 语句？

向我的服务器实例发出 DELETE 请求后的日志:

Deleting a user failed (with the following) and the error has been stored in the database: POST 500 has returned an error.

127.0.0.1 - - [Mon, 19 Oct 2015 02:50:19 GMT] "DELETE /api/users?id=11 HTTP/1.1" 500 21 "http://localhost:3000/" "Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:41.0) Gecko/20100101 Firefox/41.0"

Succesfully deleted user from system and our database: { _id: '11',
  _rev: '3-e6fec584448d664476ddaf3b7e150cd7',
  EmailAddress: 'testuser@xyz.com',
  Status: 0,
  Notes: 'POST 500 has returned an error.' }

Answer 1

首先，yes，在关闭 if() {} 之前添加一个 return 语句。这很关键。

其次，您的代码遭受 callback hell 的影响，并且您应该认真考虑切换到更“现代”的替代方案，我个人最喜欢的是 promise 。 Here's a great article about this .

对于 Node ，请尝试查看 bluebird或es6-promisify