Merge two arrays of objects but with uniqueness on a certain key/value

Question

I have two Javascript arrays of objects with various keys/values.

I'm trying to achieve a new array of objects with selected keys/values from each of the original arrays, but have uniqueness on a specific key/value.

Example:

const startDate = [
   {
    name: 'John', //Don't need this
    Id: 'ae570d88-809b-45b1-bc20-69b569e361ce', //This should be the 'unique' key
    datePosted: '2020-04-04T00:01:20.000Z' //This will be the start date
   }
]

const endDate = [
   {
    name: 'James', //Don't need this
    Id: 'ae570d88-809b-45b1-bc20-69b569e361ce', //This should be the 'unique' key
    datePosted: '2021-04-04T00:01:20.000Z' //This will be the end date
   }
]

const desiredOutput = [
    {
    'ae570d88-809b-45b1-bc20-69b569e361ce': { 
        startDate: '2020-04-04T00:01:20.000Z',
      endDate: '2021-04-04T00:01:20.000Z'
    }
  }
]

const desiredOutput2 = [
    {
     Id: 'ae570d88-809b-45b1-bc20-69b569e361ce',
     startDate: '2020-04-04T00:01:20.000Z',
     endDate: '2021-04-04T00:01:20.000Z'
  }
]

I've tried using the JS spread operator but can't figure out the renaming of the key to startDate/endDate and adding both to the same object within the array based on uniqueness of the 'Id' key.

Either of the two desiredOutputs would work great

Answer 1

You can map over the startDate array and find the endDate based on the Id .

 const startDate = [ { name: 'John', //Don't need this Id: 'ae570d88-809b-45b1-bc20-69b569e361ce', //This should be the 'unique' key datePosted: '2020-04-04T00:01:20.000Z' //This will be the start date } ] const endDate = [ { name: 'James', //Don't need this Id: 'ae570d88-809b-45b1-bc20-69b569e361ce', //This should be the 'unique' key datePosted: '2021-04-04T00:01:20.000Z' //This will be the end date } ] const desiredOutput = startDate.map((startObj) => { const foundEndDate = endDate.find((endObj) => endObj.Id === startObj.Id); return { Id: startObj.Id, startDate: startObj.datePosted, endDate: foundEndDate.datePosted, }; }); console.log(desiredOutput);

Answer 2

You could take an object with same Id as key and merge the two arrays.

 const startDate = [{ name: 'John', Id: 'ae570d88-809b-45b1-bc20-69b569e361ce', datePosted: '2020-04-04T00:01:20.000Z' }], endDate = [{ name: 'James', Id: 'ae570d88-809b-45b1-bc20-69b569e361ce', datePosted: '2021-04-04T00:01:20.000Z' }], result = Object.entries(Object.entries({ startDate, endDate }).reduce((r, [k, v]) => { v.forEach(o => r[o.Id] = {...r[o.Id], [k]: o.datePosted }) return r; }, {})).map(a => Object.fromEntries([a])); console.log(result);

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