JavaScript promises changing question

[edwardsmarkf]

hello all, first time on this forum.

i have serious problems trying to wrap my head around promises, so i have decided to just keep a couple of working examples around so i can refer back to those. here is an example i was able to put together:

const firstPromise = (promiseInput) => {
    return new Promise( (resolve, reject) =>  {       
      console.log(promiseInput);
      let returnStuff = promiseInput + ' - parameter passed into first promise. '  ;
      setTimeout( () => {
          console.log ('waiting a half-second, resolving: ' + returnStuff);
          resolve  (returnStuff);
      },500 );
        // we could use the "reject" function if this promise failed!
    })
}

const secondPromise = (promiseInput) => {
    return new Promise( (resolve, reject) =>  {       
      console.log(promiseInput);
      let returnStuff = promiseInput + ' - parameter passed into second promise. ' ;
      setTimeout( () => {
          console.log ('waiting a half-second, resolving: ' + returnStuff);
          resolve  (returnStuff);
      },500 );
    })
}

const thirdPromise = (promiseInput) => {
    return new Promise( (resolve, reject) =>  {       
      console.log(promiseInput);
      let returnStuff = promiseInput + ' - parameter passed into third promise. ' ;
      setTimeout( () => {
          console.log ('waiting a half-second, resolving: ' + returnStuff);
          resolve  (returnStuff);
      },500 );
    })
}

firstPromise('one')
  .then(  value => { return secondPromise (value + ' two')    })
  .then(  value => { return thirdPromise  (value + ' three')  })
  .then(  value => { console.log(' FINAL result: ' + value)   })
  .catch( error => { console.log(' ERROR! ' + error )         })
  ;

this is just intended to demonstrate three different promises chained together, just doing a "setTimeout" as an example. I would appreciate any opinions on my example, anything i am missing? etc.

thank you all very much.

 

[edwardsmarkf]

i received some excellent feedback from sitepoint:

Promises feedback

hello all - first time posting here. i would like somebody else knowledgeable with promises to have a look at my code example & see if this is correct or not. the code is attempting to simulate three tasks and share parameters. this will be my working example for future projects. thank you...

www.sitepoint.com

const firstPromise = (promiseInput) => {
    return new Promise( (resolve, reject) =>  {        
      console.log(promiseInput);
      let returnStuff = promiseInput + ' - parameter passed into first promise. '  ;
      setTimeout( () => {
          console.log ('waiting a half-second, resolving: ' + returnStuff);
          resolve  (returnStuff);
      },500 );
        // we could use the "reject" function if this promise failed!
    })
}
                               // shorter version per "windbeneathmywings"
const secondPromise = (promiseInput) => new Promise( (resolve, reject) =>  {        
      console.log(promiseInput);
      let returnStuff = promiseInput + ' - parameter passed into second promise. ' ;
      setTimeout( () => {
          console.log ('waiting a half-second, resolving: ' + returnStuff);
          resolve  (returnStuff);
      },500 );
})


const thirdPromise = (promiseInput) => new Promise( (resolve, reject) =>  {        
      console.log(promiseInput);
      let returnStuff = promiseInput + ' - parameter passed into third promise. ' ;
      setTimeout( () => {
          console.log ('waiting a half-second, resolving: ' + returnStuff);
          resolve  (returnStuff);
      },500 );
})



firstPromise('one')
  .then(  value => { return secondPromise (value + ' two')    })
  .then(  value =>          thirdPromise  (value + ' three')   )  // shorter version per "windbeneathmywings"
  .then(  value =>          console.log(' FINAL result: ' + value)   )
  .catch( error => { console.log(' ERROR! ' + error )         })
  ;