node.js - 如何在 Promise 中间返回响应给客户端？

Question

例如，

Comments.findOne({user: req.user.id}).exce()
.then(function(comment) {
  if(comment) {
    // how to make this return immediately and break the rest then?
    return res.json({error: 'Already commented'});
  } else {
    return Posts.findOne({postId: req.params.id}).exec();
  }
})
.then(function(post) {
  if(post) {
    var comment = new Comment({user: req.user.id, data: req.body.comment})
    return {post: post, comment: comment.save()};
  } else {
    return res.json({error: 'Post not exist'});
  }
})
.then(function(data) {
  post.comments.push(comment._id);
  return post.save();
});
.then(function(post) {
  return res.json({ok: 1})
})
.catch(function(e)) {
  return res.json(error: e);
});

这个 promise 写对了吗？这种 promise 怎么写？回调/ promise 是一个令人头疼的问题......

Answer 1

您正在使用 Bluebird ，它支持 cancellation .这是一个例子:

var Promise = require('bluebird');
// enable cancellation
Promise.config({
    cancellation: true
});

// store your promise chain
var myPromise = Promise.resolve().then(() => {
    return 'foo';
}).then((res) => {
    console.log(res);
    // call cancel on the chain when needed
    myPromise.cancel();
    return res;
}).then((res) => {
    // this will not be executed
    console.log(res + '2');
});