等待承诺 - NodeJs

Question

我正在尝试根据 leadId.length 为变量 myleadId 赋值。目标是 myleadId 在这一步之后会有一个值来继续下一步。问题是当 leadId.length <= 0（其他条件）时 myleadId 是 undefined。

app.post('/sendMessage2agent', async (req, res) => {
  getEnterpriseIDbyContact(req.body.recipient, knex).then((enterpriseId) => {
    getLeadIDbyContact(req.body.sender, knex).then((leadId) => {
      var myleadId;
      if (leadId.length > 0) {                  
        myleadId = leadId;  //works great!
      } else {
        getChannelIdByName(req.body.channel, knex).then((channelId) => {        
          return createLeadOnEnterprise(req.body.sender, enterpriseId, channelId, knex).then((newleadId) => {       
            console.log('newleadId: ' + newleadId); //newleadId is 5
            myleadId = [{'id': newleadId}]; //doesn't work :(
            return;
          });                               
        });                 
      }                         
    
      console.log('myleadId: ' + JSON.stringify(myleadId)); // myleadId is undefined when leadId.length>0 is false. I expect myleadId=[{'id': 5}]
    });     

    res.json(req.body);
  });
});

Answer 1

问题是您没有等待您的承诺。这样，他们将在与您的 console.log 不同的时间完成。您还应该看到消息 myleadId: ... 出现在控制台中的 newleadId: ... 之前。这是因为 promise 是异步执行的。所以他们让其他代码在他们执行的时候继续执行。为确保在继续执行主函数之前等待承诺，您应该使用 await。有了它，您还可以删除 .then 回调以提高可读性。

app.post('/sendMessage2agent', async (req, res) => {
  const enterpriseId = await getEnterpriseIDbyContact(req.body.recipient, knex);
  const leadId = await getLeadIDbyContact(req.body.sender, knex);
  let myleadId;
  if (leadId.length > 0) {                   
    myleadId = leadId;
  } else {
    const channelId = await getChannelIdByName(req.body.channel, knex);
    const newleadId = await createLeadOnEnterprise(req.body.sender, enterpriseId, channelId, knex);  
    console.log('newleadId: ' + newleadId);
    myleadId = [{'id': newleadId}];
  }                           
  
  console.log('myleadId: ' + JSON.stringify(myleadId));
      
  res.json(req.body);
});

等待承诺 - NodeJs

Await promise - NodeJs

node.js

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