UnhandledPromiseRejectionWarning This error originated either by throwing inside of an async function without a catch block

Question

I am getting following error in my Node-Express App      UnhandledPromiseRejectionWarning  Unhandled promise rejection  This   error originated either by throwing inside of an async function   without a catch block  or by rejecting a promise which was not handled   with  catch     rejection id  4    To say the least  I have created a helper function which looks something like this   const getEmails    userID  targettedEndpoint  headerAccessToken    gt        return axios get base url   userID   targettedEndpoint     headers    Authorization     Bearer   headerAccessToken            catch error   gt    throw error       and then I am importing this helper function   const gmaiLHelper   require       helper gmail helper     and calling it inside my api route like this  router get   emailfetch   authCheck  async  req  res    gt        listing messages in users mailbox    let emailFetch   await gmaiLHelper getEmails req user  doc profile id     messages   req user accessToken     catch error   gt    throw error     emailFetch   emailFetch data   res send emailFetch       From my end  I think I am handling the error by using catch block    Question  Can someone explain me why I am getting the error and how can I fix it

User · Answer

I resolve the problem  It s very simple   if do you checking care the problem may be because the auxiliar variable has whitespace  Why   I don t know but yus must use the trim   method and will resolve the problem

User · Answer

catch error   gt    throw error   is a no-op  It results in unhandled rejection in route handler   As explained in this answer  Express doesn t support promises  all rejections should be handled manually   router get   emailfetch   authCheck  async  req  res  next    gt      try       listing messages in users mailbox      let emailFetch   await gmaiLHelper getEmails req user  doc profile id     messages   req user accessToken      emailFetch   emailFetch data     res send emailFetch      catch  err        next err

User · Answer

You are catching the error but then you are re throwing it  You should try and handle it more gracefully  otherwise your user is going to see 500  internal server  errors   You may want to send back a response telling the user what went wrong as well as logging the error on your server   I am not sure exactly what errors the request might return  you may want to return something like   router get   emailfetch   authCheck  async  req  res    gt      try       let emailFetch   await gmaiLHelper getEmails req user  doc profile id     messages   req user accessToken        emailFetch   emailFetch data       res send emailFetch       catch error          res status error response status        return res send error message                This code will need to be adapted to match the errors that you get from the axios call   I have also converted the code to use the try and catch syntax since you are already using async

User · Answer

I suggest removing the below code from getMails    catch error   gt    throw error     In your main function you should put await and related code in Try block and also add one catch block where you failure code     you function gmaiLHelper getEmails should return a promise which has reject and resolve in it   Now while calling and using await put that in try catch block remove the  catch  as below   router get   emailfetch   authCheck  async  req  res    gt        listing messages in users mailbox  try    let emailFetch   await gmaiLHelper getEmails req user  doc profile id     messages   req user accessToken    catch  error         your catch block code goes here

[javascript] UnhandledPromiseRejectionWarning: This error originated either by throwing inside of an async function without a catch block

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