Unraveling functions from a JavaScript promise in a web application using ExpressJS and NeDB

Question

Unraveling functions from a JavaScript promise in a web application using ExpressJS and NeDB

I have successfully implemented code that retrieves all users from my neDB-promisses:

const fetchAllUsers = (res) => {
    db.find({})
        .sort({ name: 1 })
        .exec()
        .then(
            (content) => {
                res.status(200).json(content);
            },
            (err) => {
                res.status(400).json(err);
            }
        );
};

Now, I am aiming to optimize this code to prevent future redundancy in CRUD functions. I envision something like the following:

...
.then(successFunctionCall, failureFunctionCall)
...

I considered designing a separate module named successFunctionCall/failureFunctionCall, but I am faced with the challenge of needing to invoke res within it to define the response JSON and status code. Is there a more efficient approach to accomplishing this?

Thank you.

javascript express promise nedb

Answer 1

Answer №1

If you want to make use of functional programming concepts like currying, you can apply it to your functions. By passing the res parameter as a handler, you create a new function that will be ready to receive either the content or err:

const successFunctionCall = res => content => 
  res.status(200).json(content);

const failureFunctionCall = res => err => 
  res.status(400).json(err);

const getUsers = (res) => {
  db.find({})
      .sort({ name: 1 })
      .exec()
      .then(
        successFunctionCall(res),
        failureFunctionCall(res)
      );
};

Answer 2

If you want to make use of functional programming concepts like currying, you can apply it to your functions. By passing the res parameter as a handler, you create a new function that will be ready to receive either the content or err:

const successFunctionCall = res => content => 
  res.status(200).json(content);

const failureFunctionCall = res => err => 
  res.status(400).json(err);

const getUsers = (res) => {
  db.find({})
      .sort({ name: 1 })
      .exec()
      .then(
        successFunctionCall(res),
        failureFunctionCall(res)
      );
};

Answer 3

Answer №2

To prevent redundancies in CRUD operations, one possible solution is to organize your concerns differently. Here's a basic outline of what I mean.

const usersDb = {} // instance of your user database here

const findAllSortedBy = db => (...args) => db.find({}).sort(...args).exec()

const findAllUsersSortedBy = findAllSortedBy(usersDb)

const success = res => content => res.status(200).json(content)

const failure = res => err => res.status(400).json(err)

const getUsers = res => {
  findAllUsersSortedBy({ name: 1 })
    .then(success(res))
    .catch(failure(res))
}

Below demonstrates the getUsers function as part of an express route handler.

const getUsers = (req, res) => {
  findAllUsersSortedBy({ name: 1 })
    .then(success(res))
    .catch(failure(res))
}

router.get('/users', getUsers)

Answer 4

To prevent redundancies in CRUD operations, one possible solution is to organize your concerns differently. Here's a basic outline of what I mean.

const usersDb = {} // instance of your user database here

const findAllSortedBy = db => (...args) => db.find({}).sort(...args).exec()

const findAllUsersSortedBy = findAllSortedBy(usersDb)

const success = res => content => res.status(200).json(content)

const failure = res => err => res.status(400).json(err)

const getUsers = res => {
  findAllUsersSortedBy({ name: 1 })
    .then(success(res))
    .catch(failure(res))
}

Below demonstrates the getUsers function as part of an express route handler.

const getUsers = (req, res) => {
  findAllUsersSortedBy({ name: 1 })
    .then(success(res))
    .catch(failure(res))
}

router.get('/users', getUsers)

Unraveling functions from a JavaScript promise in a web application using ExpressJS and NeDB

Answer №1

Answer №2

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