Parse an array and add elements in an another array and return the new array

Question

I would like to add element an array according to another array. I do something like this with Javascript but the result is always empty:

list2 = []

list1.forEach(element => { 
  doSomething1()
    .then( something1 => { return doSomething2(something1) } )
    .then( something2 => { return doSomething3(something2) } )
    .then( something3 => if (something3 != null) { list2.push(element) } )

})

console.log(list2) // always empty

Can you help me?

You can simply do `if (condition)` instead, but to help you with your issue, what exactly `condition` is seems important. You can probably also shorten this with `.filter()` btw. — , Dec 14 '20 at 13:23
Also you probably want to use `filter` as it is the builtin to do exactly what you are doing — Martí, Dec 14 '20 at 13:25
Please create a [mcve] by adding a sample of the input and the expected output. — adiga, Dec 14 '20 at 13:36
Duplicate: https://stackoverflow.com/questions/23667086/why-is-my-variable-unaltered-after-i-modify-it-inside-of-a-function-asynchron — , Dec 14 '20 at 13:56

score 0 · Answer 1 · answered Dec 14 '20 at 13:23

0

Than your condition most likely never resolves to true. You can debug by adding a console.log above the expression and see if any of the conditions are met. Otherwise the code looks fine.

If your forEach callback is async you will have to make sure you create an array of promises and wait for all of them to resolve (await Promise.all(...)).

answered Dec 14 '20 at 13:23

Bitmonk

61
3

The question doesn't contain enough information to post a useful answer. – Dec 14 '20 at 13:24
Well he posted a theoretical question so I answered theoretically.. But I guess you're right. Will keep that in mind for other answers in the future. – Bitmonk Dec 14 '20 at 13:37
OP has just fixed their question and you hit the nail on the head, however that means OP's question is a duplicate: https://stackoverflow.com/questions/23667086/why-is-my-variable-unaltered-after-i-modify-it-inside-of-a-function-asynchron – Dec 14 '20 at 13:56
Thank you for all your answer. I will take time to understand the explanation in the duplicated post and understand this asynchronicity. – Joker Dec 14 '20 at 14:01

Parse an array and add elements in an another array and return the new array

1 Answers1