如何使这个功能成为一个承诺？

Question

路由

app.get('/api/users/:username', (req, res) => { 
    let username = req.params.username; 
    findUserInApi(username) 
    .then(foundUser => { 
     if (foundUser) { 
     res.status(403).send('User not found in api yet'); 
     }else{ 
     res.json(foundUser); 
     } 
    }); 
}); 

我想findUserInApi是一个承诺，因为我需要等待的获取就是这样函数内部发生的事情我使用快递。

这是findUserInApi

const findUserInApi = (username) => { 
    findChattersPerRole() 
    .then(chattersPerRole => { 
     console.log(`${username} should\'ve been added by now...`); 
     //console.log(chattersPerRole); 
     let wantedUser = find(chattersPerRole, {username}); 
     if (!wantedUser) { 
     console.log(`${wantedUser} wasn't found m8`); 
     return Promise.resolve(null); 
     } 
     console.log('wanteduser is: ', wantedUser); 
     getUserByUsername(wantedUser.username) 
     .then(foundUser => { 
      console.log('founduser is: ', foundUser); 
      return Promise.resolve(foundUser); 
     }); 
    }); 
}; 

我以前只是返回null时未找到或foundUser时被发现，但我想通过返回Promise.resolve做出承诺了出来。我不知道如何得到这个固定的...

Answer 1

您需要返回您的整个承诺链，就像这样：

const findUserInApi = (username) => { 
    return findChattersPerRole() 
    .then(chattersPerRole => { 
     console.log(`${username} should\'ve been added by now...`); 
     //console.log(chattersPerRole); 
     let wantedUser = find(chattersPerRole, {username}); 
     if (!wantedUser) { 
     console.log(`${wantedUser} wasn't found m8`); 
     return Promise.resolve(null); 
     } 
     console.log('wanteduser is: ', wantedUser); 
     getUserByUsername(wantedUser.username) 
     .then(foundUser => { 
      console.log('founduser is: ', foundUser); 
      return Promise.resolve(foundUser); 
     }); 
    }); 
}; 

注意在return findChattersPerRole().then()加入return。

但是，您嵌套承诺链。这是一种反模式。此外，如在评论中提到的，你不需要在.then()使用Promise.resolve()，它会自动应用。你的代码可以重构为这样的：

const findUserInApi = (username) => { 
    return findChattersPerRole() 
    .then(chattersPerRole => { 
     console.log(`${username} should\'ve been added by now...`); 
     //console.log(chattersPerRole); 
     return find(chattersPerRole, {username}); 
    }) 
    .then(wantedUser => { 
     if (wantedUser) { 
     console.log('wanteduser is: ', wantedUser); 
     return getUserByUsername(wantedUser.username); 
     } 
     else console.log(`${wantedUser} wasn't found m8`); 
    }) 
    .then(foundUser => { 
     if (foundUser) console.log('founduser is: ', foundUser); 
     return foundUser; 
    }); 
};