ask-for-promise

2.0.3 • Public • Published

Ask for Promise


Ask for Promise

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Decouple promises from their 'resolve' and 'reject' functions and make posible to use them with any javascript function ( sync or async). 'Ask-for-promise' also provide sugar syntax for some long statements.

'Ask-for-promise' provides also an option to set a ttl ( time to live) for the promise. If time is up promise will close with timeout message.

// standard promise pattern
let standardTask = new Promire ( (resolve,reject) => {
       // ... wrap everything related to the promise inside this function
       // when promise resolve - call resolve (result)
       // or call reject ( result )
    })

// after promise:
standardTask.then ( item => {
  // where 'item' is a 'result' argument sent from 'resolve' or 'reject' function. 
})



// askForPromise pattern
let askTask = askForPromise()
/* 
  askTask is an object that contains
  {
     promise    - Promise itself
     done       - function : Resolve function
     cancel     - function : Reject function
     onComplete - function : Sugar synax for askTask.promise.then
     timeout    - function : Set time to live for the promise
  }

  You can complete the promise anywhere in your code by writing:
  askTask.done(result)

  Or reject promise by:
  askTask.cancel(result)
*/

// after promise:
askTask.onComplete ( item => { 
// where 'item' is a 'result' argument sent from 'done' or 'cancel' function. 
})


// Execute a list of promise functions in sequence
let task = askForPromise.sequence ( [ function1, function2, function3 ] )
// where function1, function2, function3 are functions that return a promise
// function1 will be executed first, then function2 and function3
task.onComplete ( result => {
            // result is an array of results from all promises
   })


// Execute a list of promise functions in parallel
let task = askForPromise.all ( [ function1, function2, function3 ] )
// where function1, function2, function3 are functions that return a promise
// function1, function2 and function3 will be executed in parallel
task.onComplete ( result => {
            // result is an array of results from all promises in same order as they are in the array
   })

Installation

Install by writing in your terminal:

npm install ask-for-promise

Once it has been installed, it can be used by writing this line of JavaScript:

import askForPromise from 'ask-for-promise'

Examples

Simple promise

let task = askForPromise()

asyncFunction ( someArgument, ( err, r ) => task.done ( 'task complete' )   )

task.onComplete ( r => console.log(r)   )

// Method 'onComplete' is sugar syntax for 'task.promise.then'.
// task.promise.then ( r => { console.log ( r ) })

AskForPromise will return an object. Property task.promise will contain promise it self. Resolve function is available as task.done and reject function as task.cancel. Completion of asyncFunction will complete the promise with 'task complete' argument and will print a console message 'task complete'.

Let's do a Promise.race without using Promise.race.

let task = askForPromise()

async_1 ( arg, ( err, r) => task.done('1') )
async_2 ( arg, ( err, r) => task.done('2') )

task.onComplete ( r => console.log(r)   )
// It's equal of:
// task.promise.than ( r => console.log ( r )   )

It's almost the same as previous example - right?

Long Promise Chain

Let's see how looks long chain of promises:

// Keep definition of all promises together.
let prepareFolders  = askForPromise()
let writeFiles      = askForPromise()
let updateInterface = askForPromise()

// myFS is a dummy library that works with files.
myFS.makeFolders ( folders, ( err , r ) => prepareFolders.done() )

prepareFolders
 .onComplete ( () => {
                  myFS.writeFiles ( files , () => writeFiles.done() )
                  return writeFiles.promise
              })
.then ( () => {
                 updateInterface ()  // if it's not async.
                 updateInterface.done()
                 return updateInterface.promise
   })
.then ( () => {
                 console.log('DONE')
   })

Promise with Timeout

let final;
const task = askForPromise().timeout ( 2000, 'expire' );
// setTimeout: .timeout ( ttl, 'expireMessage'). ttl is time to live in milliseconds

task.onComplete ( result => {
    if ( result === 'expire' ) final = 'timeout'                    // ... it's after timeout
    else                       final = 'success resolved promise'
})

Promise All

Promise all by providing array of data. Here is the example:

  const files = [ 'info.txt', 'general.txt', 'about.txt' ]

  let writeFile = askForPromise ( files )

  files.forEach ( (file,i) => {
          fs.writeFile ( file,'dummy text', () => writeFile[i].done() )
       })

writeFile.onComplete ( () => console.log ( 'DONE' )   )
  

/*
Last statement is equivalent of:
Promise
   .all ( writeFile.promises )
   .then ( () => console.log ( 'DONE' )   )
*/

When function askForPromise get argument will return array of askForPromises object and property 'promises' will contain array of all promises.

Control of single promise and many promises

With 'ask-for-promise' asking for one or many promises have almost same syntax. There is some code sample to illustrate this:

  // ask for single promise
     let singlePromise = askForPromise ()

 // ask for list of promises
    let listOfItems = [ 'first', 'second', 'third' ]
    let manyPromises = askForPromise ( listOfItems )

 /* 
     manyPromises statement is short version of this:
     let temp  = listOfItems.map ( item => askForPromise ()   )
     let manyPromises = temp.map ( o => o.promise )
 */


 // Promise complete for single promise
    singlePromise.onComplete ( (r) => { console.log (r)   })

 // All promises for the array are completed.
    manyPromises.onComplete ( (r) => { console.log (r)   })

More

For more examples please visit "test" folder of the project.

External Links

Credits

'ask-for-promise' was created by Peter Naydenov.

License

'ask-for-promise' is released under the MIT License.

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