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Using Async/await in Express

Zell Liew 🤗 on October 02, 2019

Have you noticed you write a lot of asynchronous code in Express request handlers? This is normal because you need to communicate with the database...

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Mateus Amorim • Oct 2 '19

some things to note here:

I remember seeing in a article that try / catch blocks are not minified, haven't tested it out yet, but it's something to be careful about.
While you can use try / catch blocks, note that:
1. The async function returns a Promise
2. You usually would have the request handler declared in a controller file and have services functions handle the operations.
3. Promises can handle errors.

So you could also do things like this:



// user/services/user.service.getAll.ts
export default async function getAllUsers(filter: string, page: number): Promixe<IUser[]> {
   //...
}

// user/controllers/user.get.controller.ts
/*
* controller documentation...
*/
async function userGetController(req, res, next): Promise<void> {
   let { filter, page } = req.query;
   filter = filter || '';
   page = parseInt(page) || 1;
   const users = await getAllUsers(filter, page)
   .then(users => res.json(users))
   .catch(function getAllUsersControllerError(e) {
     let status = 500;
     let errorObject: IApiError = {
       //...
     }

     const returnedApiError = !!e.status;

     if (returnedApiError) {
       status = e.status;
       errorObject = e;
     }

     res.status(status).json(errorObject);
   });
}

// user/user.router.ts
app.get('/users', userGetController);

// or if you want to be even more safe

app.get('/users', function userGetRoute(req, res, next): Promise<void> {
  return userGetController(req, res, next).catch(e => {
     // do something...
  });
});
```

ogrotten • Oct 2 '19

Thank you SO MUCH for not using the wholly NOT real world settimeout() in your examples. Here's something that I can read thru and see actually applied.

Mikael Hadler • Oct 2 '19

Amazing, thank you!