有条件地退出承诺链而不会抛出错误

Question

在我的节点js应用程序中，我试图创建一个需要几个异步步骤的注册路径。在早期阶段，有一种情况是我想停下来，然后回复一条消息，但我对混合条件融入承诺感到困惑。

我的具体问题是在下面的伪代码注释：

router.post('/register', function(req, res, next) { 
    var identity = req.body.identity; 
    var password = req.body.password; 

    // can't register without a reservation 
    hasReservation(identity).then(function(hasReservation) { 
     if (hasReservation) { return register(identity, password); } 
     else { 
      // stuck here: I want to say: 
      res.json({ registered: false, reason: "missing reservation" }); 
      // and then I want to stop further promises 
      // but this isn't an error, I don't want to throw an error here 
     } 
    }).then(function(user) { 
     // in my app, registering an existing user is okay 
     // I just want to reset a few things about the user and save 
     // but I don't want to be here if there's no reservation 
     if (user) { 
      user.foo = 'bar'; 
      return user.save().then(function() { return user; }); 
     } else { 
      return register(identity, password); 
     } 
    }).then(function(user) { 
     // I want to do more asynch stuff here 
    }).then(function(result) { 
     res.json(result); 
    }).catch(function(error) { 
     res.status(500).json(error); 
    }); 
}); 

我怎么能有条件地“挽救”是第一个承诺完成后，未抛出错误？

Answer 1

如果寄存器（身份，密码）返回一个承诺，你可以按如下重新组织代码：

router.post('/register', function(req, res, next) { 
    var identity = req.body.identity; 
    var password = req.body.password; 

    // can't register without a reservation 
    hasReservation(identity) 
    .then(function(hasReservation) { 
     if (hasReservation) { 
      return register(identity, password) 
      .then(function(user) { 
       // in my app, registering an existing user is okay 
       // I just want to reset a few things about the user and save 
       // but I don't want to be here if there's no reservation 
       if (user) { 
        user.foo = 'bar'; 
        return user.save().then(function() { return user; }); 
       } else { 
        return register(identity, password); 
       } 
      }) 
      .then(function(user) { 
       // I want to do more asynch stuff here 
      }) 
      .then(function(result) { 
       res.json(result); 
      }) 
     } else { 
      // stuck here: I want to say: 
      res.json({ registered: false, reason: "missing reservation" }); 
      // and then I want to stop further promises 
      // but this isn't an error, I don't want to throw an error here 
     } 
    }) 
    .catch(function(error) { 
     res.status(500).json(error); 
    }); 
}); 

否则，如果寄存器（..）只是返回一个值，包寄存器的第一个实例（......）在Promise.resolve

 return Promise.resolve(register(identity, password))