NodeJS conditional request before the real request

Question

In my code I have to login a user with username and password. But if the user sends his e-mail instead of his username, I have to resolve it with another request.

This is what the code looks like:

exports.auth = (request, response, next) ->
 username = request.body.username
 if request.body.email
 users.findByEmail request.body.email, (error, result) ->
 return next new InternalServerError(error) if error
 username = result[0].username
 auth.auth username, request.body.password, (error, result) ->
 return next new InternalServerError(error) if error
 response.json responseData
 else
 auth.auth username, request.body.password, (error, result) ->
 return next new InternalServerError(error) if error
 response.json responseData

As you can see there are 3 duplicate lines.

Does anyone know a good code style do make this better? Maybe with Promises? Async Waterfall? Waitfor?

Answer 1

Promises would make sense to me, but first step would be to extract stuff into functions.

You don't really need promises for this, though. Here's one way to just do it with plain callbacks:

exports.auth = (request, response, next) ->
 getUsername = (request, cb) ->
 email = request.body.email
 return cb null, request.body.username unless email
 users.findByEmail email, (error, result) ->
 return cb new InternalServerError(error) if error
 cb null, result[0].username
 getUsername (err, username) ->
 return next err if err
 auth.auth username, request.body.password, (err, json) ->
 return next err if err
 response.json json