Exploring an array using bluebird promises

Question

Exploring an array using bluebird promises

I am currently facing an issue where I need to iterate over an array containing promises. My goal is to multiply all the values in the array by 2 and then return the updated array:


var Bluebird = Promise.noConflict();
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function processArray(arr) {
    return Bluebird.each(arr, function(value) {
        return value = value * 2;
    }).then(function(updatedArr) {
        console.log('--done--');
        console.log(updatedArr);
        // should return [2, 4, 6, 8, 10, 12, 14, 16, 18];
    });
}

processArray(arr);

However, my function seems to be returning the original array instead of the updated one. Can someone please assist me with this? Here's a link to my fiddle for reference:

http://jsfiddle.net/mpo4yrmu/71/

Thank you in advance!

javascript promise

Answer 1

Answer №1

Recommendation: Replace the usage of .each with .map.

While .each does not pay attention to the return value, .map certainly does.

Code Playground: http://jsfiddle.net/free_soul/mpo4yrmu/73/

var Bluebird = Promise.noConflict()
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function loopThroughArray(arr) {
  return Bluebird.map(arr, function(value) {
    return value = value * 2;
  }).then(function(arr) {
    console.log('--done--');
    console.log(arr);
    // Expected output: [2, 4, 6, 8, 10, 12, 14, 18, 19];
  });
}

loopThroughArray(arr);

Answer 2

Recommendation: Replace the usage of .each with .map.

While .each does not pay attention to the return value, .map certainly does.

Code Playground: http://jsfiddle.net/free_soul/mpo4yrmu/73/

var Bluebird = Promise.noConflict()
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function loopThroughArray(arr) {
  return Bluebird.map(arr, function(value) {
    return value = value * 2;
  }).then(function(arr) {
    console.log('--done--');
    console.log(arr);
    // Expected output: [2, 4, 6, 8, 10, 12, 14, 18, 19];
  });
}

loopThroughArray(arr);

Answer 3

Answer №2

let PromiseFree = Promise.noConflict()
let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function iterateOverArray(numbers) {
    return PromiseFree.map(numbers, function(num) {
        return num = num * 2;
    }).then(function(result) {
        console.log('--completed--');
        console.log(result);
        // expected output: [2, 4, 6, 8, 10, 12, 14, 16, 18];
    });
}

iterateOverArray(numbers);

Make use of .map method to reach your objective as demonstrated above.

Why would using .each not be suitable in this scenario?

Response: The each function operates as an iterator, iterating over an array or an array of promises, whereas the map function also iterates over an array but it waits for the values returned from each iteration and stores those return values in an array, which can be accessed in the subsequent then block.

Answer 4

let PromiseFree = Promise.noConflict()
let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function iterateOverArray(numbers) {
    return PromiseFree.map(numbers, function(num) {
        return num = num * 2;
    }).then(function(result) {
        console.log('--completed--');
        console.log(result);
        // expected output: [2, 4, 6, 8, 10, 12, 14, 16, 18];
    });
}

iterateOverArray(numbers);

Make use of .map method to reach your objective as demonstrated above.

Why would using .each not be suitable in this scenario?

Response: The each function operates as an iterator, iterating over an array or an array of promises, whereas the map function also iterates over an array but it waits for the values returned from each iteration and stores those return values in an array, which can be accessed in the subsequent then block.

Answer 5

Answer №3

Bluebird.each() keeps the original array unchanged, hence why the initial array is being printed.

Bluebird.each

...Maintains the original array as is; this function is designed for side effects. If the iterator function produces a promise or a thenable, the resolution of that promise is awaited before moving on to the next iteration.

http://bluebirdjs.com/docs/api/promise.each.html

The recommended approach would be to utilize Javascript's built-in Array.prototype.map():

//Example using promises
...function(arr) {
    console.log('done!');
    console.log(arr.map(function(element) {
      return element * 2;
    }));
   }

Answer 6

Bluebird.each() keeps the original array unchanged, hence why the initial array is being printed.

Bluebird.each

...Maintains the original array as is; this function is designed for side effects. If the iterator function produces a promise or a thenable, the resolution of that promise is awaited before moving on to the next iteration.

http://bluebirdjs.com/docs/api/promise.each.html

The recommended approach would be to utilize Javascript's built-in Array.prototype.map():

//Example using promises
...function(arr) {
    console.log('done!');
    console.log(arr.map(function(element) {
      return element * 2;
    }));
   }

Answer 7

Answer №4

the result you are receiving is not a direct reference value. You can achieve it in a similar manner, but keep in mind that the values of the array will be modified.

var Bluebird = Promise.noConflict()
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function iterateOverArray(arr) {
     Bluebird.each(arr, function(value, i) {
     arr[i] = arr[i] * 2;
  }).then(function(arr) {
    console.log('--completed--');
    console.log(arr);
    // expected output: [2, 4, 6, 8, 10, 12, 14, 18, 19];
  });
}

iterateOverArray(arr);

Answer 8

the result you are receiving is not a direct reference value. You can achieve it in a similar manner, but keep in mind that the values of the array will be modified.

var Bluebird = Promise.noConflict()
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];

function iterateOverArray(arr) {
     Bluebird.each(arr, function(value, i) {
     arr[i] = arr[i] * 2;
  }).then(function(arr) {
    console.log('--completed--');
    console.log(arr);
    // expected output: [2, 4, 6, 8, 10, 12, 14, 18, 19];
  });
}

iterateOverArray(arr);

Exploring an array using bluebird promises

Answer №1

Answer №2

Answer №3

Answer №4

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