In mongoose.js after every query the functions returns (error, result). I would like to write function of my own that does the same.
I thought the answer was to use promises so I wrote this
login: (user) ->
q.Promise (resolve, reject, notify) ->
console.log resolve
if _.has(user, 'password')
dashboard.users.find(user).exec().then (err, results) ->
if err then reject("Error occurred with the database")
if results then resolve(results) else reject("User not found")
else
reject("A password is required for login")
Auth.login(testuser).then (d) ->
console.log d, "done"
but after research I found that this is an anti pattern and the code does not work (promise is never resolved/rejected). So now I am not sure what to do.
In mongoose.js after every query the functions returns (error, result). I would like to write function of my own that does the same.
I thought the answer was to use promises so I wrote this
login: (user) ->
q.Promise (resolve, reject, notify) ->
console.log resolve
if _.has(user, 'password')
dashboard.users.find(user).exec().then (err, results) ->
if err then reject("Error occurred with the database")
if results then resolve(results) else reject("User not found")
else
reject("A password is required for login")
Auth.login(testuser).then (d) ->
console.log d, "done"
but after research I found that this is an anti pattern and the code does not work (promise is never resolved/rejected). So now I am not sure what to do.
Share Improve this question edited Nov 26, 2014 at 6:37 grasshopper asked Nov 26, 2014 at 6:28 grasshoppergrasshopper 9584 gold badges14 silver badges30 bronze badges 5-
How do you know the promise is never resolved/rejected? I don't see that you're using the actual promise anywhere. Did you mean to return the promise from the
login()method? – jfriend00 Commented Nov 26, 2014 at 6:35 - yes I did I forgot to add that code I'll add it now – grasshopper Commented Nov 26, 2014 at 6:36
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Like I said, you have to return the promise from the
login()method so the callers oflogin()can use it. – jfriend00 Commented Nov 26, 2014 at 6:38 - my original code had this but it is still the same result you are saying I should have deferred.promise returned at the end right? – grasshopper Commented Nov 26, 2014 at 6:51
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Avoid the
Promiseconstructor antipattern! – Bergi Commented Aug 21, 2022 at 14:13
1 Answer
Reset to default 2To return errors from functions as promises, there are generally two ways to produce rejected promises:
- The
rejectfunction of your Promise library - Throwing an exception in a
thencallback or returning a rejected promise from it will reject the resulting promise
This has the same effect as building a promise for an async function that calls its node-style callback with an error argument. Your code would be rewritten to
login: (user) ->
if _.has(user, 'password')
q(dashboard.users.find(user).exec()).then (results) ->
if results
results
else
throw new Error("User not found")
, (err) ->
throw new Error("Error occurred with the database")
else
q.reject("A password is required for login")