javascript - 多重 promise - 在哪里解决？

Question

我刚开始 promise 。

我正在使用nodejs promisify，因此我将以下内容声明为Redis的 promise

const { promisify } = require('util');
const getAsync = promisify(client.get).bind(client);
const hmsetAsync = promisify(client.hmset).bind(client);
const hsetAsync = promisify(client.hset).bind(client);
const incrAsync = promisify(client.incr).bind(client);
const smembersAsync = promisify(client.smembers).bind(client);
const keysAsync = promisify(client.keys).bind(client);
const sismemberAsync = promisify(client.sismember).bind(client);

我有以下函数，但我不知道放置解析(消息)的正确位置

function sendMessage(senderId = '', roomId = '', text = '', type='text') {

        var message = {}
        return new Promise( function (resolve, reject) {

    if (senderId == '') {
        reject('Invalid Characters in Sender Id or Sender Id is empty.');
    }


    if (roomId == '') {
        reject('Invalid Characters in Room Id or Room Id is empty.');
    }

    if (text == '') {
        console.log('Text:' ,text);
        reject('Invalid Characters in Text or Text is empty.');
    }
            //Check if Room Exist

            keysAsync('room-'+roomId).then((value) => {

                value == '' && reject('Room '+roomId+ ' does not exist.');
                sismemberAsync('roomuser-'+roomId, senderId).then((ismember)=> {
                    ismember == 0 && reject('User ' + senderId + ' is not a member of room ' + roomId);

                    const datetime = new Date();
                    incrAsync('messageId')
                    .then((id) => {
                        //Create the message Hash
                        hmsetAsync('messsage:'+id, 'id', id, 'roomId', roomId, 'senderId', senderId, "created", datetime, "text", text);
                        //add message to Set
                        saddAsync('roommessages-'+roomId, id);

                        message = { id: id, roomId: roomId, senderId: senderId, created: datetime, text: text }
                        resolve(message) //If i place here i don't get the resolve.

                    }).catch(err => reject(err))

                }).catch(err => reject(err))

            }).catch(err => reject(err))
        })
    }

然后我尝试像这样调用该函数

tools.sendMessage(3, 4, 'Does this work?','text').then((result)=> {
  console.log('Send Message Result => ',result);
}).catch(err => { 
  console.log(err)
});

如果我将解析(消息)放在现在的位置，则上述 promise 不会解析，并且“发送消息结果”根本不会显示。

如果我将其放置在链 promise 之外，则 var 消息将返回一个空对象{}

我的问题:在这种需要多次 Promise 调用的函数中，我应该将解析放在哪里，因为我需要等待多次 Redis 检查？

我有许多函数，需要先执行所有 redis 调用，然后才能继续执行下一步操作。

Answer 1

我可能会考虑按如下方式重构您的代码。如果您需要临时捕获错误 .then()然后阶段使用 onrejected 回调。

function sendMessage(senderId = '', roomId = '', text = '', type='text') {
  return keysAsync('room-'+roomId)
         .then(value => value === '' ? Promise.reject('Room '+roomId+ ' does not exist.')
                                     : sismemberAsync('roomuser-'+roomId, senderId))
         .then(ismember => ismember === 0 ? Promise.reject('User ' + senderId + ' is not a member of room ' + roomId)
                                          : incrAsync('messageId'))
         .then(id => { var datetime =new Date();
                       hmsetAsync('messsage:'+id, 'id', id, 'roomId', roomId, 'senderId', senderId, "created", datetime, "text", text);
                       saddAsync('roommessages-'+roomId, id);
                       return { id: id, roomId: roomId, senderId: senderId, created: datetime, text: text };
                     })
         .then(message => doSomethingWith(message))
         .catch(errorHandler);
}

在上面的代码中我移动了new Date()到实际使用的下一级，但是如果由于某种原因您需要 datetime原文.then()如您问题中所示的阶段，那么您不妨执行以下操作；

function sendMessage(senderId = '', roomId = '', text = '', type='text') {
  return keysAsync('room-'+roomId)
         .then(value => value === '' ? Promise.reject('Room '+roomId+ ' does not exist.')
                                     : sismemberAsync('roomuser-'+roomId, senderId))
         .then(ismember => ismember === 0 ? Promise.reject('User ' + senderId + ' is not a member of room ' + roomId)
                                          : Promise.all([incrAsync('messageId'), new Date()]))
         .then(([id, datetime]) => { hmsetAsync('messsage:'+id, 'id', id, 'roomId', roomId, 'senderId', senderId, "created", datetime, "text", text);
                                     saddAsync('roommessages-'+roomId, id);
                                     return { id: id, roomId: roomId, senderId: senderId, created: datetime, text: text };
                                   })
         .then(message => doSomethingWith(message))
         .catch(errorHandler);
}