how to combine all data in separated session storage?

Is it possible to combine all session storage into one?

I have these three arrays which I pushing into storage because I will access them later.

The reason why I'm doing this is that the array I need is on a separated page. So I can't combine the array before pushing it into storage.

Here's what i have tried.

function FnOne() {
    let arrayInFnOne = [
      {
        'id': 1,
        'Choices': 'Cheeta'
      },
       {
        'id': 2,
        'Choices': 'Eagle'
       },
       {
        'id': 3,
        'Choices': 'Elephant'
       },
       {
        'id': 4,
        'Choices': 'Duck'
       },
       {
        'id': 5,
        'Choices': 'Deer'
       }
    ]
   let FNDataOne = sessionStorage.setItem('FNoneData', JSON.stringify(arrayInFnOne));
  }

function FnTwo(){
  let arrayInFnTwo = [
        {
          'id': 6,
          'Choices': 'Eggplant'
        },
         {
          'id': 7,
          'Choices': 'Tomato'
         },
         {
          'id': 8,
          'Choices': 'Potato'
         },
         {
          'id': 9,
          'Choices': 'String beans'
         },
         {
          'id': 10,
          'Choices': 'Squash'
         }
      ]
     let FNDataTwo = sessionStorage.setItem('FNtwoData', JSON.stringify(arrayInFnTwo));
}

function FnThree(){
let arrayInFnThree = [
        {
          'id': 11,
          'Choices': 'Paper'
        },
         {
          'id': 12,
          'Choices': 'Pencil'
         },
         {
          'id': 13,
          'Choices': 'Monitor'
         },
         {
          'id': 14,
          'Choices': 'Pentel Pen'
         },
         {
          'id': 15,
          'Choices': 'Wire'
         }
      ]
     let FNDataThree = sessionStorage.setItem('FNthreeData', JSON.stringify(arrayInFnThree));
}

document.querySelector('button').addEventListener('click', () => {
    let finalData = sessionStorage.setItem('FinalDataAns', concat(FNDataOne,FNDataTwo,FNDataThree))
  console.log(finalData);
})

<button>
Save
</button>

Solution

You can get these 3 arrays from session storage and then parse them to Javascript objects. After all, you can use those objects to concat into the final array.

function FnOne() {
  let arrayInFnOne = [{
      'id': 1,
      'Choices': 'Cheeta'
    },
    {
      'id': 2,
      'Choices': 'Eagle'
    },
    {
      'id': 3,
      'Choices': 'Elephant'
    },
    {
      'id': 4,
      'Choices': 'Duck'
    },
    {
      'id': 5,
      'Choices': 'Deer'
    }
  ]

  //you cannot get returned value from `setItem`
  //let FNDataOne = sessionStorage.setItem('FNoneData', JSON.stringify(arrayInFnOne));
  sessionStorage.setItem('FNoneData', JSON.stringify(arrayInFnOne));
}

function FnTwo() {
  let arrayInFnTwo = [{
      'id': 6,
      'Choices': 'Eggplant'
    },
    {
      'id': 7,
      'Choices': 'Tomato'
    },
    {
      'id': 8,
      'Choices': 'Potato'
    },
    {
      'id': 9,
      'Choices': 'String beans'
    },
    {
      'id': 10,
      'Choices': 'Squash'
    }
  ]

  //you cannot get returned value from `setItem`
  //let FNDataTwo = sessionStorage.setItem('FNtwoData', JSON.stringify(arrayInFnTwo));
  sessionStorage.setItem('FNtwoData', JSON.stringify(arrayInFnTwo));
}

function FnThree() {
  let arrayInFnThree = [{
      'id': 11,
      'Choices': 'Paper'
    },
    {
      'id': 12,
      'Choices': 'Pencil'
    },
    {
      'id': 13,
      'Choices': 'Monitor'
    },
    {
      'id': 14,
      'Choices': 'Pentel Pen'
    },
    {
      'id': 15,
      'Choices': 'Wire'
    }
  ]
  //you cannot get returned value from `setItem`
  //let FNDataThree = sessionStorage.setItem('FNthreeData', JSON.stringify(arrayInFnThree));
  sessionStorage.setItem('FNthreeData', JSON.stringify(arrayInFnThree));
}

//for demo purpose
FnOne()
FnTwo()
FnThree()

document.querySelector('button').addEventListener('click', () => {
  //use `getItem` to get string data in session storage
  //and `JSON.parse` them
  //finally, concat all arrays
    const concatArray = [].concat(['FNoneData', 'FNtwoData', 'FNthreeData'].map(key => JSON.parse(sessionStorage.getItem(key))))
  //stringify to store in session storage
  const stringConcatArray = JSON.stringify(concatArray)
  sessionStorage.setItem('FinalDataAns', stringConcatArray)

  //get saved data from sessionStorage
  const finalData = sessionStorage.getItem('FinalDataAns');
  //have to parse back to Javascript object
  console.log(JSON.parse(finalData));
})

<button>
Save
</button>