在我的node js应用程序中，我试图创建一个需要执行一些异步步骤的注册路由。在较早的步骤中，有一种情况我想停止并只返回一条消息，但是我对将条件混入承诺中感到困惑。
我的具体问题在以下伪代码中的注释中：
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);
});
});
在第一个承诺完成后，如何有条件地“纾困”而不抛出错误？
如果register（identity，password）返回一个promise，则可以按以下方式重新组织代码：
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register（..）仅返回一个值，则将Register（...）的FIRST实例包装在Promise中。
return Promise.resolve(register(identity, password))
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