Does not work as expected when work with Promise.all

[Gcaufy]

Here is the demo code

const sequential = require('promise-sequential');
const array = [1,2,3,4,5];

const makePromise = function(item) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(item)
    }, 1000);
  });
};

const makePromiseAll = function(item) {
  return Promise.all([
    new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve('a' + item);
      }, 1000)
    }),
    new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve('b' + item);
      }, 1000)
    }),
  ])
}

const makeFunc = function(fn) {
  return function (item) {
    return function(prevResp, resp, count) {
      return fn(item);
    }
  }
};

// Result expected
Promise.all(array.map(item => makePromise(item))).then(res => console.log('promise all result: ', res));
sequential(array.map(item => makeFunc(makePromise)(item))).then(res => console.log('sequential result: ', res));


// Result not expected
Promise.all(array.map(item => makePromiseAll(item))).then(res => console.log('promise all with promise all result: ', res));
sequential(array.map(item => makeFunc(makePromiseAll)(item))).then(res => console.log('sequential with promise all result: ', res));

Here is the result:

promise all result:  [ 1, 2, 3, 4, 5 ]
promise all with promise all result:  [
  [ 'a1', 'b1' ],
  [ 'a2', 'b2' ],
  [ 'a3', 'b3' ],
  [ 'a4', 'b4' ],
  [ 'a5', 'b5' ]
]
sequential result:  [ 1, 2, 3, 4, 5 ]
sequential with promise all result:  [
  'a1', 'b1', 'a2',
  'b2', 'a3', 'b3',
  'a4', 'b4', 'a5',
  'b5'
]

When sequential a simple promise array, it will get the result as expected. But when it work with Promise.all, it make the result array flat.

Is there any way to keep the array?

[aminnairi]

I guess I fixed it by using what I described here in this article I wrote on DEV (I replaced the require with the definition of sequential I gave on the said article but named PromiseExtra.sequence).

const sequential = promises => {
  return promises.reduce((previousPromise, currentPromise) => {
    return previousPromise.then(previousState => {
      return currentPromise(previousState).then(newState => {
        return [
          ...previousState,
          newState
        ];
      });
    });
  }, Promise.resolve([]));
};

const array = [1,2,3,4,5];

const makePromise = function(item) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(item)
    }, 1000);
  });
};

const makePromiseAll = function(item) {
  return Promise.all([
    new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve('a' + item);
      }, 1000)
    }),
    new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve('b' + item);
      }, 1000)
    }),
  ])
}

const makeFunc = function(fn) {
  return function (item) {
    return function(prevResp, resp, count) {
      return fn(item);
    }
  }
};

// Result expected
Promise.all(array.map(item => makePromise(item))).then(res => console.log('promise all result: ', res));
sequential(array.map(item => makeFunc(makePromise)(item))).then(res => console.log('sequential result: ', res));


// Result not expected
Promise.all(array.map(item => makePromiseAll(item))).then(res => console.log('promise all with promise all result: ', res));
sequential(array.map(item => makeFunc(makePromiseAll)(item))).then(res => console.log('sequential with promise all result: ', res));

promise all result:  [ 1, 2, 3, 4, 5 ]
promise all with promise all result:  [
  [ 'a1', 'b1' ],
  [ 'a2', 'b2' ],
  [ 'a3', 'b3' ],
  [ 'a4', 'b4' ],
  [ 'a5', 'b5' ]
]
sequential result:  [ 1, 2, 3, 4, 5 ]
sequential with promise all result:  [
  [ 'a1', 'b1' ],
  [ 'a2', 'b2' ],
  [ 'a3', 'b3' ],
  [ 'a4', 'b4' ],
  [ 'a5', 'b5' ]
]

I didn't intend to make it a library but if this repository is dead I can make one in a blink, tell me if you are interested.