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
– julBayonna, Commented Jun 9, 2022 at 7:36
Could you please edit your question to match your examples to your code; is it selected or sleected? Is it true or false? — Phil
– Phil, Commented Jun 9, 2022 at 7:44
You still have selected: true in your first code snippet and false everywhere else — Phil
– Phil, Commented Jun 9, 2022 at 7:54

Nick Parsons · Accepted Answer · 2022-06-09 08:02:52Z

2

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);

edited Jun 9, 2022 at 8:02

answered Jun 9, 2022 at 7:35

Nick Parsons

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Nick · Accepted Answer · 2022-06-09 07:53:30Z

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 9, 2022 at 7:53

answered Jun 9, 2022 at 7:36

Nick

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6 Comments

Andy Over a year ago

Small fyi: selected should be false.

Phil Over a year ago

It should also be sleected according to OP's example 😉

Nick Over a year ago

@Andy Ironically I copied it from OPs code...

Nick Over a year ago

@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 :)

Phil Over a year ago

FileNotFound

|

Andy · Accepted Answer · 2022-06-09 07:37:06Z

1

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);

answered Jun 9, 2022 at 7:37

Andy

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