Can promises have multiple arguments to onFulfilled

Question

I m following the spec here and I m not sure whether it allows onFulfilled to be called with multiple arguments   For example   promise   new Promise function onFulfilled  onRejected       onFulfilled  arg1    arg2         such that my code   promise then function arg1  arg2                     would receive both arg1 and arg2   I don t care about how any specific promises implementation does it  I wish to follow the w3c spec for promises closely

User · Answer

Here is a CoffeeScript solution     I was looking for the same solution and found seomething very intersting from this answer  Rejecting promises with multiple arguments  like  http  in AngularJS  the answer of this guy Florian  promise   deferred promise  promise success    fn  - gt    promise then  data  - gt     fn data payload  data status   additional  42     return promise  promise error    fn  - gt    promise then null   err  - gt      fn err    return promise  return promise    And to use it   service get   success  arg1  arg2  arg3  - gt          gt  arg1 is data payload  arg2 is data status  arg3 is the additional object service get   error  err  - gt          gt  err

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De-structuring Assignment in ES6 would help here For Ex   let  arg1  arg2    new Promise  resolve  reject    gt        resolve  argument1  argument2

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Since functions in Javascript can be called with any number of arguments  and the document doesn t place any restriction on the onFulfilled   method s arguments besides the below clause  I think that you can pass multiple arguments to the onFulfilled   method as long as the promise s value is the first argument      2 2 2 1 it must be called after promise is fulfilled  with promise   s value as its first argument

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As far as I can tell reading the ES6 Promise specification and the standard promise specification theres no clause preventing an implementation from handling this case - however its not implemented in the following libraries    RSVP promise   L516-544  Q promise   787    I assume the reason for them omiting multi arg resolves is to make changing order more succinct  i e  as you can only return one value in a function it would make the control flow less intuitive  Example   new Promise function resolve  reject       return resolve 5  4       then function x y       console log y      return x    we can only return 1 value here so the next then will only have 1 argument     then function x y        console log y

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The fulfillment value of a promise parallels the return value of a function and the rejection reason of a promise parallels the thrown exception of a function  Functions cannot return multiple values so promises must not have more than 1 fulfillment value

User · Answer

You can use E6 destructuring   Object destructuring   promise   new Promise function onFulfilled  onRejected       onFulfilled  arg1  value1  arg2  value2        promise then   arg1  arg2     gt                      Array destructuring   promise   new Promise function onFulfilled  onRejected       onFulfilled  value1  value2        promise then   arg1  arg2     gt

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Great question  and great answer by Benjamin  Kris  et al - many thanks   I m using this in a project and have created a module based on Benjamin Gruenwald s code  It s available on npmjs   npm i -S promise-spread   Then in your code  do   require  promise-spread      If you re using a library such as any-promise  var Promise   require  any-promise    require  promise-spread   Promise     Maybe others find this useful  too

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To quote the article below    then  takes two arguments  a callback for a success case  and another for the failure case  Both are optional  so you can add a callback for the success or failure case only    I usually look to this page for any basic promise questions  let me know if I am wrong  http   www html5rocks com en tutorials es6 promises

User · Answer

I m following the spec here and I m not sure whether it allows onFulfilled to be called with multiple arguments     Nope  just the first parameter will be treated as resolution value in the promise constructor  You can resolve with a composite value like an object or array      I don t care about how any specific promises implementation does it  I wish to follow the w3c spec for promises closely    That s where I believe you re wrong  The specification is designed to be minimal and is built for interoperating between promise libraries  The idea is to have a subset which DOM futures for example can reliably use and libraries can consume  Promise implementations do what you ask with  spread for a while now  For example   Promise try function        return   Hello   World           spread function a b c       console log a b c       Hello World          With Bluebird  One solution if you want this functionality is to polyfill it    if   Promise prototype spread        Promise prototype spread   function  fn            return this then function  args                return Promise all args      wait for all            then function args              this is always undefined in A  complaint  but just in case             return fn apply this  args                           This lets you do   Promise resolve null  then function        return   Hello   World            spread function a b c       console log a b c             With native promises at ease fiddle  Or use spread which is now  2018  commonplace in browsers   Promise resolve   Hello   World        then   a b c     gt      console log a b c             Or with await   let  a  b  c    await Promise resolve   hello    world

[javascript] Can promises have multiple arguments to onFulfilled?

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