Iterate Promise

Iterate Promise is an npm package used for synchronizing async loop calls based on 'deasync' blocking mechanism by calling Node.js event loop.

Problem

While looping through an iterable set, a problem arises when we wish to perform an async task on each item of the set and also perform a task in same sequential order with the response received.

Solution

Iterate promise offers a simple and easy solution for this problem.

• forEach function

  forEach(iterableSet, onEach, afterEach)

  • iterableSet - A data structure that can be iterated.
  • onEach - Work to perform on each loop iteration (must return a promise)
    • The function will have a single position variable which the iterate-promise package will return (current position of the loop).
    • The function must return a new Promise with resolve having no params and reject with the error object (see example).
  • afterEach - Work to perform after each loop async code successfully executes.
    • The function will have a single position variable which the iterate-promise package will return (current position of the loop).

  Example -

  Using ES6 syntax

  let iPromise = require('iterate-promise');
  
  iPromise.forEach(array, (position) => { //forEach function
      return new Promise(
          function (resolve, reject) {
            
              request({                   //async call
                  uri: array[position],
                  method: "GET"
                    
              }, (error, result, body) => {
                                          //response from async call
                  if (error) {
                      reject(error);
                  } else {
                      newArray.push(JSON.parse(body));
                      resolve();
                  }
                    
              });
          }
      );
        
  }, (position) => {                   //afterEach function
    
      console.log(position);
        
  }).then(() => {                     //after the complete loop successfully executes
    
      console.log("Done");        
        
  }).catch((errorObject) => {         //if it fails (Read below)
    
      console.log(errorObject.position);
      console.log(errorObject.error);
        
  });

  • If an iteration inside the loop fails the whole function will be rejected.
  • Inside the catch , an errorObject will be returned which will be a json object containing two keys
    • position - position at which the loop fails
    • error - the error returned by the async function

• forEachWorking function

  forEachWorking(iterableSet, onEach, onEachError,afterEach)

  • onEachError - If an error occurs on single item of the iterable set.

  Example -

  Using ES6 syntax

  let iPromise = require('iterate-promise');
   
  iPromise.forEachWorking(array, (position) => { //forEach function
         return new Promise(
             function (resolve, reject) {
                 //todo                  
             }
         );
           
     },(position,error) => {                   //onEachError function
                 
         console.log(position + error);
                     
     },(position) => {                   //afterEach function
           
     }).then(() => {                     //after the complete loop successfully executes
                                
     }).catch((errorObject) => { 
       
     });

  Note : If there is a user defined error anywhere in any function , the execution directly goes to the catch function without working any further

Versions

• v1.1.0

  New : forEachWorking function will continue working even if a single iteration fails

• v1.0.1

  Initial release - containing the basic forEach function only.

Special Thanks

• Deasync
• Promise

Contact

• Twitter - @dawnimpulse

License (ISC)

ISC Licence

Copyright 2018 Saksham (DawnImpulse)

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted,
provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE
OR PERFORMANCE OF THIS SOFTWARE.