Break promise chain and call a function based on the step in the chain where it is broken rejected

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Update   To help future viewers of this post  I created this demo of pluma s answer    Question   My goal seems fairly straightforward     step 1     then function         return step 2        function         stepError 1       return  q reject            then function           function         stepError 2            function step n        var deferred    q defer          fail on step 1      n     1    deferred reject     deferred resolve        return deferred promise        function stepError n        console log n          The problem here is that if I fail on step 1  both stepError 1  AND stepError 2  are fired  If I don t return  q reject then stepError 2  won t be fired  but step 2  will  which I understand  I ve accomplished everything except what I m trying to do   How do I write promises so that I can call a function on rejection  without calling all of the functions in the error chain  Or is there another way to accomplish this   Here s a live demo so you ve got something work with   Update   I kind of have solved it  Here  I am catching the error at the end of the chain and passing the data to reject data  so that I will know what issue to handle in the error function  This actually doesn t meet my requirements because I don t want to depend on the data  It would be lame  but in my case it would be cleaner to pass an error callback to the function rather than to depend on the returned data to determine what to do   Live demo here  click    step 1     then function         return step 2           then function         return step 3           then false       function x          stepError x                function step n        console log  Step   n       var deferred    q defer         n     1    deferred reject n    deferred resolve n       return deferred promise        function stepError n        console log  Error   n

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var s   1  start    then function        return step s         then function         return step s         then function         return step s         then 0  function e      console log s-1          http   jsbin com EpaZIsIp 20 edit  Or automated for any number of steps   var promise   start    var s   1  var l   3  while l--        promise   promise then function             return step s               promise then 0  function e      console log s-1          http   jsbin com EpaZIsIp 21 edit

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The reason your code doesn t work as expected is that it s actually doing something different from what you think it does   Let s say you have something like the following   stepOne    then stepTwo  handleErrorOne   then stepThree  handleErrorTwo   then null  handleErrorThree     To better understand what s happening  let s pretend this is synchronous code with try catch blocks   try       try           try               var a   stepOne              catch e1                a   handleErrorOne e1                     var b   stepTwo a         catch e2            b   handleErrorTwo e2             var c   stepThree b     catch e3        c   handleErrorThree e3       The onRejected handler  the second argument of then  is essentially an error correction mechanism  like a catch block   If an error is thrown in handleErrorOne  it will be caught by the next catch block  catch e2    and so on   This is obviously not what you intended   Let s say we want the entire resolution chain to fail no matter what goes wrong   stepOne    then function a        return stepTwo a  then null  handleErrorTwo      handleErrorOne   then function b        return stepThree b  then null  handleErrorThree         Note  We can leave the handleErrorOne where it is  because it will only be invoked if stepOne rejects  it s the first function in the chain  so we know that if the chain is rejected at this point  it can only be because of that function s promise    The important change is that the error handlers for the other functions are not part of the main promise chain  Instead  each step has its own  sub-chain  with an onRejected that is only called if the step was rejected  but can not be reached by the main chain directly    The reason this works is that both onFulfilled and onRejected are optional arguments to the then method  If a promise is fulfilled  i e  resolved  and the next then in the chain doesn t have an onFulfilled handler  the chain will continue until there is one with such a handler   This means the following two lines are equivalent   stepOne   then stepTwo  handleErrorOne  stepOne   then null  handleErrorOne  then stepTwo    But the following line is not equivalent to the two above   stepOne   then stepTwo  then null  handleErrorOne    Angular s promise library  q is based on kriskowal s Q library  which has a richer API  but contains everything you can find in  q   Q s API docs on GitHub could prove useful  Q implements the Promises A  spec  which goes into detail on how then and the promise resolution behaviour works exactly   EDIT   Also keep in mind that if you want to break out of the chain in your error handler  it needs to return a rejected promise or throw an Error  which will be caught and wrapped in a rejected promise automatically   If you don t return a promise  then wraps the return value in a resolve promise for you    This means that if you don t return anything  you are effectively returning a resolved promise for the value undefined

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When rejecting you should pass an rejection error  then wrap step error handlers in a function that checks whether the rejection should be processed or  rethrown  until the end of the chain       function mocking steps function step i        i        console log  step   i       return q resolve i         function mocking a failing step function failingStep i        i        console log  step    i      will fail         var e   new Error  Failed on step     i       e step   i      return q reject e         error handler function handleError e       if  error breakChain               handleError has already been called on this error             see code bellow          log  errorHandler  skip handling            return q reject error                firs time this error is past to the handler     console error  errorHandler  caught error     error message          process the error                        error breakChain   true      return q reject error         run the steps  will fail on step 4    and not run step 5 and 6    note that handleError of step 5 will be called    but since we use that error breakChain boolean    no processing will happen and the error will    continue through the rejection path until done       step 0     1    catch handleError     then step     2    catch handleError     then step     3    catch handleError     then failingStep      4 fail    catch handleError     then step     5    catch handleError     then step     6    catch handleError     done function          log  success arguments   arguments        function  error          log  Done  chain broke at step     error step           What you d see on the console    step 1 step 2 step 3 step 4  will fail  errorHandler  caught error  Failed on step 4  errorHandler  skip handling errorHandler  skip handling Done  chain broke at step 4   Here is some working code https   jsfiddle net 8hzg5s7m 3   If you have specific handling for each step  your wrapper could be something like         simple wrapper to check if rejection    has already been handled     param function real error handler     function createHandler realHandler        return function error            if  error breakChain                return q reject error                     realHandler error           error breakChain   true          return q reject error                 then your chain  step1    catch createHandler handleError1Fn    then step2   catch createHandler handleError2Fn    then step3   catch createHandler handleError3Fn    done function        log  success       function  error        log  Done  chain broke at step     error step

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The best solution is to refactor to your promise chain to use ES6 await s   Then you can just return from the function to skip the rest of the behavior   I have been hitting my head against this pattern for over a year and using await s is heaven

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Found Promise prototype catch   examples on MDN below very helpful    The accepted answer mentions then null  onErrorHandler  which is basically the same as catch onErrorHandler        Using and chaining the catch method  var p1   new Promise function resolve  reject      resolve  Success         p1 then function value      console log value       Success     throw  oh  no       catch function e      console log e       oh  no      then function      console log  after a catch the chain is restored       function        console log  Not fired due to the catch            The following behaves the same as above p1 then function value      console log value       Success     return Promise reject  oh  no        catch function e      console log e       oh  no      then function      console log  after a catch the chain is restored       function        console log  Not fired due to the catch              Gotchas when throwing errors     Throwing an error will call the catch method most of the time var p1   new Promise function resolve  reject      throw  Uh-oh         p1 catch function e      console log e       Uh-oh           Errors thrown inside asynchronous functions will act like uncaught errors var p2   new Promise function resolve  reject      setTimeout function         throw  Uncaught Exception         1000        p2 catch function e      console log e      This is never called         Errors thrown after resolve is called will be silenced var p3   new Promise function resolve  reject      resolve      throw  Silenced Exception         p3 catch function e       console log e      This is never called           If it is resolved    Create a promise which would not call onReject var p1   Promise resolve  calling next     var p2   p1 catch function  reason          This is never called     console log  catch p1         console log reason        p2 then function  value        console log  next promise s onFulfilled       next promise s onFulfilled        console log value      calling next       function  reason        console log  next promise s onRejected        console log reason

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If at any point you return Promise reject  something   you will be thrown in the catch block to the promise   promiseOne    then  result    gt        if   result          return Promise reject  No result              return          catch  err    gt        console log err           If the first promise does not return any result you will only get  No result  in the console

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What you need is a repeating  then   chain with a special case to start and a special case to finish   The knack is to get the step number of the failure case to ripple through to a final error handler    Start  call step 1  unconditionally  Repeating pattern  chain a  then   with the following callbacks    success  call step n 1  failure  throw the value with which the previous deferered was rejected or rethrow the error   Finish  chain a  then   with no success handler and a final error handler    You can write the whole thing out longhand but it s easier to demonstrate the pattern with named  generalised functions    function nextStep n        return step n   1      function step n        console log  step     n       var deferred    q defer         n     3    deferred reject n    deferred resolve n       return deferred promise     function stepError n        throw n      function finalError n        console log  finalError     n     step 1       then nextStep  stepError       then nextStep  stepError       then nextStep  stepError       then nextStep  stepError       then nextStep  stepError       then null  finalError        see demo  Note how in step    the deferred is rejected or resolved with n  thus making that value available to the callbacks in the next  then   in the chain  Once stepError is called  the error is repeatedly rethrown until it is handled by finalError

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If I understand correctly  you want only the error for the failing step to show  right   That should be as simple as changing the failure case of the first promise to this   step 1  then function  response        step 2      function  response        stepError 1       return response     then          By returning  q reject   in the first step s failure case  you re rejecting that promise  which causes the errorCallback to be called in the 2nd then

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Attach error handlers as separate chain elements directly to the execution of the steps              Handle errors for step 1  step 1  then null  function     stepError 1   return  q reject        then function                         Attach error handler for step 2                       but only if step 2  is actually executed   return step 2  then null  function     stepError 2   return  q reject            then function                         Attach error handler for step 3                       but only if step 3  is actually executed   return step 3  then null  function     stepError 3   return  q reject              or using catch               Handle errors for step 1  step 1  catch function     stepError 1   return  q reject        then function                         Attach error handler for step 2                       but only if step 2  is actually executed   return step 2  catch function     stepError 2   return  q reject            then function                         Attach error handler for step 3                       but only if step 3  is actually executed   return step 3  catch function     stepError 3   return  q reject              Note  This is basically the same pattern as pluma suggests in his answer but using the OP s naming

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Use a SequentialPromise Module  Intention  Provide a module whose responsibility is to execute requests sequentially  while tracking the current index of each operation in an ordinal manner  Define the operation in a Command Pattern for flexibility   Participants   Context  The object whose member method performs an operation  SequentialPromise  Defines an execute method to chain  amp  track each operation  SequentialPromise returns a Promise-Chain from all operations performed  Invoker  Creates a SequentialPromise instance  providing it context  amp  action  and calls its execute method while passing in an ordinal list of options for each operation    Consequences  Use SequentialPromise when ordinal behavior of Promise resolution is needed  SequentialPromise will track the index for which a Promise was rejected   Implementation  clear     var http         get url            var delay   Math floor  Math random     10    even     delay   2           var xhr   new Promise exe            console log  REQUEST   url  delay           xhr then   data    gt  console log  SUCCESS     data    catch   data    gt  console log  FAILURE     data              function exe resolve  reject                var action      true   reject   false   resolve    even                setTimeout       gt  action   url  delay      1000   delay                        return xhr            var SequentialPromise   new  function SequentialPromise         var PRIVATE   this       return class SequentialPromise            constructor context  action                this index   0              this requests                    this context   context              this action   action               return this                     log               execute url     more                var   context  action  requests     this              var chain   context action  url                requests push chain               chain then   data    gt  this index    1                 if  more length  return chain then       gt  this execute    more                 return chain                           var sequence   new SequentialPromise http   get    var urls          url name space 0        url name space 1        url name space 2        url name space 3        url name space 4        url name space 5        url name space 6        url name space 7        url name space 8        url name space 9     var chain   sequence execute    urls   var promises   sequence requests   chain catch       gt  console warn  EXECUTION STOPPED at   sequence index  for   urls sequence index            console log   gt    chain  promises      Gist  SequentialPromise

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Bit late to the party but this simple solution worked for me   function chainError err      return Promise reject err      stepOne    then stepTwo  chainError   then stepThreee  chainError     This allows you to break out of the chain

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Try ro use this like libs   https   www npmjs com package promise-chain-break      db getData    then pb  data    gt        if   data someCheck              tellSomeone                All other   then  calls will be skiped         return pb BREAK             then pb      gt         then pb      gt         catch  error    gt        console error error

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If you want to solve this issue using async await    async function            try                   const response1  response2  response3         response1   await promise1            if response1               response2   await promise2                     if response2               response3   await promise3                     return  response1  response2  response3        catch  error            return

[javascript] Break promise chain and call a function based on the step in the chain where it is broken (rejected)

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