add null value for proprties which do not exist in array of objects

Question

I have a requirement where I want to add null values for properties which are non existent in the array of objects. I don't want to loop over

var data=[
    {
        "id": 1,
        "name": "John"
    },
    {
        "id": 2
    },
    {
        "id": 3
    }
]

Expected result is as follows

[
    {
        "id": 1,
        "name": "John"
    },
    {
        "id": 2,
        "name": null
    },
    {
        "id": 3,
        "name": null
    }
]

you have to loop over. even if you use `map` – cmgchess Apr 20 '23 at 08:38 — cmgchess, Apr 20 '23 at 08:38

score 0 · Answer 1 · answered Apr 20 '23 at 08:41

0

Map array so if name is undefined set it to null, otherwise leave the same value:

const result = data.map(item => ({...item, name: item.name ?? null}))

answered Apr 20 '23 at 08:41

munleashed

1,677
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3
9

score 0 · Answer 2 · answered Apr 20 '23 at 08:51

Little for each loop will do that. Also I think || would be better than ??, here is why:
When should I use ?? (nullish coalescing) vs || (logical OR)?

const data =[
    {
        "id": 1,
        "name": "John"
    },
    {
        "id": 2
    },
    {
        "id": 3
    }
]

data.forEach(set => { set.name = set.name || null })
console.log(data)

Ah sorry, didn't notice the part with the loop in the question. I still let this answer be here.

score 0 · Answer 3 · answered Apr 20 '23 at 09:55

One further option is the following, with explanatory comments in the code; this answer assumes that the keys may have to be found prior to adding them to the Object:

// the initial Array of Objects:
const data = [{
    id: 1,
    name: "John",
  },
  {
    id: 2,
  },
  {
    id: 3,
  }
],

// a simple function, declared using Arrow function syntax,
// which takes one argument, an Array of Objects:
getAllKeys = (objectArray) => {

  // we return an Array formed from a Set, by use of the
  // spread syntax and an Array literal:
    return [...new Set(
        // we form the Set from the reduced Array of Objects,
        // created using Array.prototype.reduce():
        objectArray.reduce(
          // the Array.prototype.reduce() method has the
          // arguments of 'acc' (the accumulator formed
          // by the method), and the 'curr' Object (the
          // current Object of the Array of Objects):
          (acc,curr) => {
            // within the Arrow function, we simply
            // push the keys of the current Object -
            // retrieved with Object.keys - to the
            // accumulator Array, which we then flatten
            // using Array.prototype.flat():
            acc.push(Object.keys(curr));
          return acc.flat();
        // the empty Array-literal here is the accumulator
        // used within the method:
        },[]
      )
    )];
  },
// here we use the function to retrieve an Array of the
// keys from Objects in the data Array:
keys = getAllKeys(data),

// we then use Array.prototype.map() to iterate over the
// data Array and create a new Array from that Array:
newData = data.map((obj) =>{
  // we return a new Object, created using Object.fromEntries():
    return Object.fromEntries(
    // we use Array.prototype.map() to iterate over the
    // Array of Object properties:
    keys.map(
      // 'k' is the value of the current Object property
      // ('k' standing for 'key' in this case);
      // we return a new two-part Array formed from the
      // current Object property-name, and the existing
      // property-value of the current Object's property
      // of that name, or null (if no property-value
      // exists):
      (k)=> [k, obj[k] || null]
    )
  );
});

console.log(newData);
/*
  [
    {
      id: 1,
      name: "John"
    },
    {
      id: 2,
      name: null
    },
    {
      id: 3,
      name: null
    }
  ]

*/

JS Fiddle demo.

References:

add null value for proprties which do not exist in array of objects

3 Answers3