Bluebird's Promise resolve returns undefined

Question

I'm new to Promise, so I was trying out Bluebird's Promise APIs. I have the following method that returns a Promise.try()

CheckDb - Promise Method

const Prom = require("bluebird")

..........
..........

let checkDb = () => {
 return Prom.try(() => {
   SomePromiseMethod().then(result => {
    if (//some condition) {
      let resp = { 
          res: result, 
          somethingelse : somethingelse 
      }
      return Prom.resolve(resp)
    }
    else 
      return Prom.reject(new Error("some reason"));
   }, err => {
      return Prom.reject(err);
   })
   .catch(err => {
     return Prom.reject(err);
   });
 });
}

SomeTask - Method calling the promise method

exports.someTask = () => {
      checkDb().then(resolved => {
       console.log(resolved) // coming undefined
      }, 
      rejected => {
       console.error(rejected);
      })
      .catch(err => {console.error(err)});
    }

The problem here is that the resolved component of the then method of the Promise function is returning undefined.

I looked into this and this, but couldn't figure it out.

return Prom.try({ SomePromiseMethod().then is a syntax error — baao
replace your first codeblock with this pastebin and it will work (you don't even need to require bluebird!!!) — Jaromanda X
note, .catch(err => { return Prom.reject(err); }); is just the same as not having the catch at all ... similarly with the onrejected handler above it - there's no reason for it at all — Jaromanda X
@JaromandaX It was a mistake while I was copy pasting the code. The code has always been how the example looks now. — Auro

Rafael L. Toscano Rafael L. Toscano · Accepted Answer · 2018-07-30T23:07:40

Try to return the value directly without using this Prom.resolve, like this:

...
        return SomePromiseMethod().then(result => {
            if (//some condition) {
              let resp = { 
                  res: result, 
                  somethingelse : somethingelse 
              }
              return resp
            }
            else 
              throw new Error("some reason"));
           }
    ...

If you are in the "then" method of a promise, you resolve it by returning a value, which is passed to the next "then" method in the chain.

You would use the resolve method explicitly if you had:

a defer created "by hand" and you wanted to resolve it
a promise created by you if you wanted to "promisify" something that is not a promise, like this example below:

return new Promise(function(resolve, reject) { ... resolve(value);

})

Which is not your case. (Edited this part of the answer to avoid misinterpretation)

Bluebird's Promise resolve returns undefined

1 Answers