How to pass a property from an array to each of it nested child array with lodash?

Question

Hello let's take this example :

var legitTask = [
  {
    "guid": "beb033fd-f2ca-4bde-a732-4396d560b216",
    "isActive": false,
    "friends": [
      {
        "id": 33,
        "name": "Rosalind Kaufman"
      },
      {
        "id": 41,
        "name": "Marion Armstrong"
      },
      {
        "id": 52,
        "name": "Sonia Baxter"
      }
    ]
  },
  {
    "guid": "2ac71ecb-4d7e-4c81-bd54-f6d17ce141a9",
    "isActive": true,
    "friends": [
      {
        "id": 023,
        "name": "Viola Gillespie"
      },
      {
        "id": 31,
        "name": "Anita Bass"
      },
      {
        "id": 12,
        "name": "Galloway Townsend"
      }
    ]
  },
  {
    "guid": "07acf598-cb57-490f-a42c-3a0ee0a543fc",
    "isActive": true,
    "friends": [
      {
        "id": 0,
        "name": "Lou Elliott"
      },
      {
        "id": 71,
        "name": "Christina Spence"
      },
      {
        "id": 82,
        "name": "Doris Garner"
      }
    ]
  }
]

Desired Final Result: Assign ONLY the isActive property of each parent to each of it friends

 [        {
            "id": 33,
            "name": "Rosalind Kaufman",
             "isActive": false
         },
         {
            "id": 41,
            "name": "Marion Armstrong",
             "isActive": false
         },
         {
            "id": 52,
            "name": "Sonia Baxter",
             "isActive": false
         }, {
            "id": 023,
            "name": "Viola Gillespie"
            "isActive": true
         },
         {
            "id": 31,
            "name": "Anita Bass"
            "isActive": true
         },
         {
            "id": 12,
            "isActive": true
            "name": "Galloway Townsend"
         },
         {
            "id": 0,
            "isActive": true,
            "name": "Lou Elliott"
         },
         {
            "id": 71,
            "isActive": true,
            "name": "Christina Spence"
         },
         {
            "id": 82,
            "isActive": true,
            "name": "Doris Garner"
         }
      ]

So my first step would be to pick the friends and the desired property :

let firstRound  = _.map(legitTask, task =>{
   return _.pick(task, ['isActive', 'friends']);
});

GREAT! I have now the desired property and each of the friends, now how to pass the property to each of the friends? (Assuming I have a BIG list so the 'best way' is a necessity, Yes I know I can loop and loop and loop, but that would really kill the performance )

🥴 Here where I'm stuck

    _.forEach(firstRound, parent =>{
         return _.map(parent.friends, task =>{
       return _.assign(task, parent.isActive);
    });

});

Answer 1

When it comes to performance, I always find that vanilla JS is faster than any library implementation. So I always prefer vanilla JS for this reason. Here, a non-lodash.js solution, that places the desired values into the array, though you can simply deep-clone your original array:

const res = legitTask
  .map(obj => {
    return obj.friends.map(friend => {
      friend.isActive = obj.isActive;
      return friend;
    });
  })
  .flat();

Alternatively, if you don't want to deepclone, you can use this implementation, which is slower, but keeps your old array intact:

const res = legitTask
  .map(obj => {
    return obj.friends.map(friend => {
      const returnObj = { ...friend };
      returnObj.isActive = obj.isActive;
      return returnObj;
    });
  })
  .flat();

Answer 2

You can try like this.

  _.reduce(legitTask, (acc, {friends, ...rest}) => acc.concat(_.map(friends, friend => ({...friend,...rest }))), [])