How can I create an object mapping from an array of strings?

Question

i am stumbling onto something that should be easy, yet i can't seem to be able to do it.

i have an array of string, and i want to map over it to create an object like so :

const monthesList = ['january', 'february', 'march', 'april', 'may']

const myState = monthesList.map(month => (
    month: {selected: false, year: 2022}
    )
  )

what i want is to get the following object :

myState ={
  january:{ 
    selected: false,
    year: 2022
  },
  february:{ 
    selected: false,
    year: 2022
  },
  march:{ 
    selected: false,
    year: 2022
  },
  april:{ 
    selected: false,
    year: 2022
  },
  may:{ 
    selected: false,
    year: 2022
  },
}

Edit: i just found the way :

const myState = monthesList.map(month => (
    {[month] : {
      selected: false,
      year: 2022
    }}
    )
  )

just need to make an object out of it, shouldn't be too hard

yes you're right, i know but it's not what was bothering me, i can easliy transfomr the array to an object — julBayonna, Jun 09 '22 at 07:36
Could you please [edit] your question to match your examples to your code; is it `selected` or `sleected`? Is it `true` or `false`? — Phil, Jun 09 '22 at 07:44
You still have `selected: true` in your first code snippet and `false` everywhere else — Phil, Jun 09 '22 at 07:54

Nick Parsons · Accepted Answer · 2022-06-09T08:02:52.740

The .map() method returns an array, but the output that you're after is an object. You need something that can convert an array of key-value pairs (ie: [key, value]) to an object. For this, we have the Object.fromEntries() method that takes an array of key-value pairs, and from it, constructs an object like so:

const monthesList = ['january', 'february', 'march', 'april', 'may'];

const myState = Object.fromEntries(monthesList.map(month => [
  month, {selected: false, year: 2022}
]));
console.log(myState);

Nick · Answer 2 · 2022-06-09T07:53:30.670

2

You can use map to generate an array of arrays with the values in each internal array being the month name and object; then use Object.fromEntries to convert that into your desired object:

const monthesList = ['january', 'february', 'march', 'april', 'may']

const myState = Object.fromEntries(
  monthesList.map(m => [m, {selected: false, year: 2022}])
)

console.log(myState)

edited Jun 09 '22 at 07:53

answered Jun 09 '22 at 07:36

Nick

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Small fyi: `selected` should be `false`. – Andy Jun 09 '22 at 07:40
It should also be `sleected` according to OP's example – Phil Jun 09 '22 at 07:40
1

@Andy Ironically I copied it from OPs code... – Nick Jun 09 '22 at 07:44
1

@Phil well, the spelling has been corrected but there's still one `true` and one `false` in the question's code... perhaps I should put in a non-binary value instead :) – Nick Jun 09 '22 at 07:54
1

[`FileNotFound`](https://thedailywtf.com/articles/what_is_truth_0x3f_) – Phil Jun 09 '22 at 07:57
@Phil ROTFL!!!! – Nick Jun 09 '22 at 07:58

score 1 · Answer 3 · answered Jun 09 '22 at 07:37

map will only return an array. Your expected output is an object. There's no need to over-complicate things - use a simple loop instead.

const list = ['january', 'february', 'march', 'april', 'may'];

const myState = {};

for (const month of list) {
  myState[month] = { selected: false, year: 2022 };
}

console.log(myState);

How can I create an object mapping from an array of strings?

3 Answers3